media: lirc: simplify gap calculation

When a driver reports a timeout, no more IR activity will be reported
until the next pulse. A space is inserted between the timeout and the
next pulse, based on ktime.

The timeout reports already a duration, so this duration should not be
added to the gap. Otherwise there is no change to the functionality.

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