drm/i915: Kill a goto from sprite disable code

Let's not use goto when a simple if suffices. This is not error handling
code or anything, so the goto looks out of place.

Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>