[media] staging: lirc_serial: Do not assume error codes returned by request_irq()

lirc_serial_probe() must fail if request_irq() returns an error, even if
it isn't EBUSY or EINVAL,

Signed-off-by: Ben Hutchings <ben@decadent.org.uk>
Signed-off-by: Mauro Carvalho Chehab <mchehab@redhat.com>