usb: Fix fall-through warnings for Clang

In preparation to enable -Wimplicit-fallthrough for Clang, fix multiple
warnings by explicitly adding multiple break/return/fallthrough
statements instead of letting the code fall through to the next
case.

Link: https://github.com/KSPP/linux/issues/115


Signed-off-by: Gustavo A. R. Silva <gustavoars@kernel.org>
Link: https://lore.kernel.org/r/a76da7ca5b4f41c13d27b298accb8222d0b04e61.1605896060.git.gustavoars@kernel.org


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>