drm/i915: Use plane->name in debug prints

We have plane->name, so let's use that in debug messages instead
of just printing the more or less useless object ID.

v2: slap on a commit message

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1464371966-15190-3-git-send-email-ville.syrjala@linux.intel.com


Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>