[media] lirc: LIRC_{G,S}ET_SEND_MODE fail if device cannot transmit

These ioctls should not succeed if the device cannot send. Also make it
clear that these ioctls should return the lirc mode, although the actual
value does not change.

Signed-off-by: Sean Young <sean@mess.org>
Reviewed-by: Andi Shyti <andi.shyti@samsung.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>