Sonypi: use synchronize_irq instead of sycnronize_sched

We know exactly what IRQ we are using, so synchronize_irq()
suits much better. Plus synchronize_sched() will not work
for us in -rt kernels.

Signed-off-by: Dmitry Torokhov <dtor@mail.ru>
Acked-by: Mattia Dongili <malattia@linux.it>