drm/i915: Use DRM_DEV_ERROR in i915_driver_load

Now that it is available we don't have to open code a similar
error message ourselves.

Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1481051053-29783-1-git-send-email-tvrtko.ursulin@linux.intel.com