drm/i915: Fix whitespace (trivial)

Signed-off-by: NBen Widawsky <benjamin.widawsky@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1451427643-7266-1-git-send-email-benjamin.widawsky@intel.comSigned-off-by: NJani Nikula <jani.nikula@intel.com>