media: cx231xx: fix RC_CORE dependency

With CONFIG_RC_CORE=m and VIDEO_CX231XX=y, we get a link failure:

drivers/media/usb/cx231xx/cx231xx-input.o: In function `cx231xx_ir_init':
cx231xx-input.c:(.text+0xd4): undefined reference to `rc_allocate_device'

This narrows down the dependency so that only valid configurations
are allowed.

Fixes: 84545d2a

 ("media: cx231xx: Remove RC_CORE dependency")

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab+samsung@kernel.org>