drm/i915; Only increment the user-pin-count after successfully pinning the bo

As along the error path we do not correct the user pin-count for the
failure, we may end up with userspace believing that it has a pinned
object at offset 0 (when interrupted by a signal for example).
Signed-off-by: NChris Wilson <chris@chris-wilson.co.uk>
Cc: stable@vger.kernel.org
Signed-off-by: NDaniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/i915_gem.c

@@ -3522,14 +3522,15 @@ i915_gem_pin_ioctl(struct drm_device *dev, void *data,
 		goto out;
 	}
 
-	obj->user_pin_count++;
-	obj->pin_filp = file;
-	if (obj->user_pin_count == 1) {
+	if (obj->user_pin_count == 0) {
 		ret = i915_gem_object_pin(obj, args->alignment, true, false);
 		if (ret)
 			goto out;
 	}
 
+	obj->user_pin_count++;
+	obj->pin_filp = file;
+
 	/* XXX - flush the CPU caches for pinned objects
 	 * as the X server doesn't manage domains yet
 	 */