V4L/DVB: saa7134: don't wait too much to generate an IR event on raw_decode

At raw_decode mode, the key is processed after the end of a timer. The
previous code resets the timer every time something is received at the IR
port. While this works fine with IR's that don't implement repeat, like
Avermedia RM-JX IR, it keeps waiting until keydown, on IR's that implement
NEC repeat command, like the Terratec yellow.

The solution is to change the behaviour to do the timeout after the first
received data.

The timeout is currently set to 15 ms, as it works fine with NEC protcocol.
It may need some adjustments to support other protocols and to better handle
spurious detections that may happen with some IR sensors.

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