usb: raw_gadget: fix compilation warnings in uapi headers

usb: raw_gadget: fix compilation warnings in uapi headers

Mark usb_raw_io_flags_valid() and usb_raw_io_flags_zero() as inline to
fix the following warnings:

./usr/include/linux/usb/raw_gadget.h:69:12: warning: unused function 'usb_raw_io_flags_valid' [-Wunused-function]
./usr/include/linux/usb/raw_gadget.h:74:12: warning: unused function 'usb_raw_io_flags_zero' [-Wunused-function]

Reported-by: kernelci.org bot <bot@kernelci.org>
Reported-by: Stephen Rothwell <sfr@canb.auug.org.au>
Signed-off-by: Andrey Konovalov <andreyknvl@google.com>
Link: https://lore.kernel.org/r/6206b80b3810f95bfe1d452de45596609a07b6ea.1584456779.git.andreyknvl@google.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>