drm: Remove two leaks of vblank reference count in error paths.

If the failing paths were hit, the vblank IRQ would never get turned off
again.

Signed-off-by: Eric Anholt <eric@anholt.net>
Acked-by: Keith Packard <keithp@keithp.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/i915/i915_irq.c

@@ -771,6 +771,7 @@ int i915_vblank_swap(struct drm_device *dev, void *data,
 		    vbl_swap->plane == plane &&
 		    vbl_swap->sequence == swap->sequence) {
 			spin_unlock_irqrestore(&dev_priv->swaps_lock, irqflags);
+			drm_vblank_put(dev, pipe);
 			DRM_DEBUG("Already scheduled\n");
 			return 0;
 		}