drm/i915: No need to save/restore irq status in intel_breadcrumbs_fake_irq

Timer callback is a known context so it is correct to always
disable interrupts.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Cc: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>