[media] staging/lirc: Fix compilation when LIRC=m

drivers/staging/lirc/lirc_bt829.c:141: undefined reference to `lirc_register_driver'
drivers/built-in.o:(.rodata+0x20f68): undefined reference to `lirc_dev_fop_read'
drivers/built-in.o:(.rodata+0x20f7c): undefined reference to `lirc_dev_fop_poll'
drivers/built-in.o:(.rodata+0x20f8c): undefined reference to `lirc_dev_fop_open'
drivers/built-in.o:(.rodata+0x20f94): undefined reference to `lirc_dev_fop_close'
drivers/built-in.o:(.rodata+0x21030): undefined reference to `lirc_dev_fop_open'
drivers/built-in.o:(.rodata+0x21038): undefined reference to `lirc_dev_fop_close'

This happens when .config is like:
	CONFIG_LIRC=m
	CONFIG_IR_LIRC_CODEC=m
	CONFIG_LIRC_STAGING=y
	CONFIG_LIRC_BT829=y

Don't allow that.

Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>