media: cec-pin: Fixed ktime_t to ns conversion

Older Kernels use a struct for ktime_t, which requires the conversion
function ktime_to_ns to be used on some places. With this patch it will
compile now also for older Kernel versions.

Signed-off-by: Jasmin Jessich <jasmin@anw.at>
Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>