Mark switch cases where we are expecting to fall through.

This patch fixes the following warning (Building: arm):

drivers/usb/host/ohci-tmio.c: In function ‘tmio_stop_hc’:
./include/linux/device.h:1499:2: warning: this statement may fall through [-Wimplicit-fallthrough=]
  _dev_err(dev, dev_fmt(fmt), ##__VA_ARGS__)
  ^~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
drivers/usb/host/ohci-tmio.c:99:4: note: in expansion of macro ‘dev_err’
    dev_err(&dev->dev, "Unsupported amount of ports: %d\n", ohci->num_ports);
    ^~~~~~~
In file included from drivers/usb/host/ohci-hcd.c:1257:0:
drivers/usb/host/ohci-tmio.c:100:3: note: here
   case 3:
   ^~~~
drivers/usb/host/ohci-tmio.c:101:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    pm |= CCR_PM_USBPW3;
       ^
drivers/usb/host/ohci-tmio.c:102:3: note: here
   case 2:
   ^~~~
drivers/usb/host/ohci-tmio.c:103:7: warning: this statement may fall through [-Wimplicit-fallthrough=]
    pm |= CCR_PM_USBPW2;
       ^
drivers/usb/host/ohci-tmio.c:104:3: note: here
   case 1:
   ^~~~
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Link: https://lore.kernel.org/r/20190729222201.GA19408@embeddedorSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>