drm/i915: Consolidate reporting of "missed breadcrumbs"

Move the setting of gpu_error->missed_irq_ring bit to a common function
so that we can get the debug logging for either path.

v2: Add %pF caller

Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/20170228085018.3225-1-chris@chris-wilson.co.uk