drm/i915: Be consistent on printing seqnos

We have had %x and %u intermixed. Bring everything in line and
use %x

Signed-off-by: Mika Kuoppala <mika.kuoppala@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>