drm/i915: Kill dev_priv->irq_received

Not sure anyone cares about this information. I suppose most people
would just look at /proc/interrupts instead.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Acked-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>