media: gpio-ir-tx: spinlock is not needed to disable interrupts

During bit-banging the IR on a gpio pin, we cannot be scheduled or have
anything interrupt us, else the generated signal will be incorrect.
Therefore, we need to disable interrupts on the local cpu. This also
disables preemption.

local_irq_disable() does exactly what we need and does not require a
spinlock.

Signed-off-by: Sean Young <sean@mess.org>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>