It failed to register device when remote keymap was not set.
Fix it to register device even keymap is NULL. In that case
just skip remote registration.

Driver should set RC_MAP_EMPTY to enable remote in case of
there is remote receiver but default keymap is unknown.
Reported-by: pierigno <pierigno@gmail.com>
Signed-off-by: Antti Palosaari <crope@iki.fi>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>