[media] sir_ir: infinite loop in interrupt handler

Since this driver does no detection of hardware, it might be used with
a non-sir port. Escape out if we are spinning.

Reported-by: kbuild test robot <fengguang.wu@intel.com>
Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab@s-opensource.com>