Mark switch cases where we are expecting to fall through.

This patch fixes the following warnings (Building: sparc defconfig):

drivers/scsi/qlogicpti.c: In function 'qlogicpti_mbox_command':
drivers/scsi/qlogicpti.c:202:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 6: sbus_writew(param[5], qpti->qregs + MBOX5);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:203:2: note: here
  case 5: sbus_writew(param[4], qpti->qregs + MBOX4);
  ^~~~
drivers/scsi/qlogicpti.c:203:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 5: sbus_writew(param[4], qpti->qregs + MBOX4);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:204:2: note: here
  case 4: sbus_writew(param[3], qpti->qregs + MBOX3);
  ^~~~
drivers/scsi/qlogicpti.c:204:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 4: sbus_writew(param[3], qpti->qregs + MBOX3);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:205:2: note: here
  case 3: sbus_writew(param[2], qpti->qregs + MBOX2);
  ^~~~
drivers/scsi/qlogicpti.c:205:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 3: sbus_writew(param[2], qpti->qregs + MBOX2);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:206:2: note: here
  case 2: sbus_writew(param[1], qpti->qregs + MBOX1);
  ^~~~
drivers/scsi/qlogicpti.c:206:10: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 2: sbus_writew(param[1], qpti->qregs + MBOX1);
          ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:207:2: note: here
  case 1: sbus_writew(param[0], qpti->qregs + MBOX0);
  ^~~~
drivers/scsi/qlogicpti.c:256:19: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 6: param[5] = sbus_readw(qpti->qregs + MBOX5);
          ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:257:2: note: here
  case 5: param[4] = sbus_readw(qpti->qregs + MBOX4);
  ^~~~
drivers/scsi/qlogicpti.c:257:19: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 5: param[4] = sbus_readw(qpti->qregs + MBOX4);
          ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:258:2: note: here
  case 4: param[3] = sbus_readw(qpti->qregs + MBOX3);
  ^~~~
drivers/scsi/qlogicpti.c:258:19: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 4: param[3] = sbus_readw(qpti->qregs + MBOX3);
          ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:259:2: note: here
  case 3: param[2] = sbus_readw(qpti->qregs + MBOX2);
  ^~~~
drivers/scsi/qlogicpti.c:259:19: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 3: param[2] = sbus_readw(qpti->qregs + MBOX2);
          ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:260:2: note: here
  case 2: param[1] = sbus_readw(qpti->qregs + MBOX1);
  ^~~~
drivers/scsi/qlogicpti.c:260:19: warning: this statement may fall through [-Wimplicit-fallthrough=]
  case 2: param[1] = sbus_readw(qpti->qregs + MBOX1);
          ~~~~~~~~~^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/scsi/qlogicpti.c:261:2: note: here
  case 1: param[0] = sbus_readw(qpti->qregs + MBOX0);
  ^~~~
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Reviewed-by: Kees Cook <keescook@chromium.org>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>