media: rc-loopback: max_timeout of UINT_MAX does not work

Any timeout larger than LIRC_VALUE_MASK cannot work for the lirc uapi.
LIRC_VALUE_MASK is about 16 seconds which is more than enough.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>