In preparation to enabling -Wimplicit-fallthrough, mark switch
cases where we are expecting to fall through.

This patch fixes the following warning:

drivers/ide/ide-floppy.c: In function ‘ide_floppy_get_capacity’:
drivers/ide/ide-floppy.c:424:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    if (!(drive->atapi_flags & IDE_AFLAG_CLIK_DRIVE))
       ^
drivers/ide/ide-floppy.c:431:3: note: here
   case CAPACITY_CURRENT:
   ^~~~

Warning level 3 was used: -Wimplicit-fallthrough=3

Notice that, in this particular case, the code comment is modified
in accordance with what GCC is expecting to find.

This patch is part of the ongoing efforts to enable
-Wimplicit-fallthrough.
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: David S. Miller <davem@davemloft.net>