drm: self_refresh: Fix a reversed condition in drm_self_refresh_helper_cleanup()

This test is flipped around so it either leads to a memory leak or a
NULL dereference.

Fixes: 1452c25b ("drm: Add helpers to kick off self refresh mode in drivers")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Sean Paul <seanpaul@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20190619100141.GA28596@mwanda

drivers/gpu/drm/drm_self_refresh_helper.c

@@ -205,7 +205,7 @@ void drm_self_refresh_helper_cleanup(struct drm_crtc *crtc)
 	struct drm_self_refresh_data *sr_data = crtc->self_refresh_data;
 
 	/* Helper is already uninitialized */
-	if (sr_data)
+	if (!sr_data)
 		return;
 
 	crtc->self_refresh_data = NULL;