drm/i915: Update i915_driver_load kerneldoc

Update i915_driver_load kerneldoc to match code.

Cc: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Joonas Lahtinen <joonas.lahtinen@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: http://patchwork.freedesktop.org/patch/msgid/1478784994-2494-2-git-send-email-joonas.lahtinen@linux.intel.com