drm/i915: drop __FUNCTION__ as argument to DRM_DEBUG_KMS

DRM_DEBUG_KMS includes printing the function name.

Signed-off-by: Christoph Jaeger <christophjaeger@linux.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>