Do not respond with -EINVAL to EVIOCGKEYCODE for not-yet-mapped
scancodes, but rather return KEY_RESERVED.

This fixes breakage with Ubuntu's input-kbd utility that stopped
returning full keymaps for remote controls.
Tested-by: NMauro Carvalho Chehab <mchehab@redhat.com>
Tested-by: NMark Lord <kernel@teksavvy.com>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>