usb: fix a few cases of -Wfallthrough

usb: fix a few cases of -Wfallthrough

The "fallthrough" pseudo-keyword was added as a portable way to denote
intentional fallthrough. Clang will still warn on cases where there is a
fallthrough to an immediate break. Add explicit breaks for those cases.

Reviewed-by: Nathan Chancellor <natechancellor@gmail.com>
Signed-off-by: Nick Desaulniers <ndesaulniers@google.com>
Link: https://lore.kernel.org/r/20201111014716.260633-1-ndesaulniers@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>