USB: always visit drivers/usb/misc/

Currently, every driver under drivers/usb/misc/ also has to be listed in
drivers/usb/Makefile. This has been forgotten more than once, and this
patch changes drivers/usb/Makefile to simply always visit
drivers/usb/misc/ when building the USB code.

Signed-off-by: Adrian Bunk <bunk@kernel.org>
Cc: Toralf Förster <toralf.foerster@gmx.de>
Acked-by: Satyam Sharma <satyam@infradead.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>