[media] staging: lirc_serial: silence GCC warning

Building lirc_serial.o triggers this GCC warning:
    drivers/staging/media/lirc/lirc_serial.c: In function '__check_sense':
    drivers/staging/media/lirc/lirc_serial.c:1301:1: warning: return from incompatible pointer type [enabled by default]
This can be trivially fixed by changing the 'sense' parameter from bool
to int. But, to be safe, we also need to make sure 'sense' will only be
-1, 0, or 1. There's no need to document the new values that are now
allowed for the 'sense' parameter, since they're basically useless.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Cc: Jarod Wilson <jarod@wilsonet.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>