drm/i915: Trim some if-else braces

Just a bit of cleanup after the previous refactoring.

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/1467212972-861-1-git-send-email-tvrtko.ursulin@linux.intel.com