drm: Set crc->opened to false before setting crc source to NULL.

to terminate the while-loop in drm_dp_aux_crc_work when
drm_dp_start/stop_crc are called in the hook to set crc source.

v3: set crc->opened to false without checking (Nick)
v2: Move spin_lock around entire crc->opened use (Daniel)

Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Harry Wentland <Harry.Wentland@amd.com>
Cc: Nick Kazlauskas <Nicholas.Kazlauskas@amd.com>
Signed-off-by: Dingchen Zhang <dingchen.zhang@amd.com>
Reviewed-by: Harry Wentland <harry.wentland@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190726173743.11641-1-dingchen.zhang@amd.com

drivers/gpu/drm/drm_debugfs_crc.c

@@ -258,6 +258,11 @@ static int crtc_crc_release(struct inode *inode, struct file *filep)
 	struct drm_crtc *crtc = filep->f_inode->i_private;
 	struct drm_crtc_crc *crc = &crtc->crc;
 
+	/* terminate the infinite while loop if 'drm_dp_aux_crc_work' running */
+	spin_lock_irq(&crc->lock);
+	crc->opened = false;
+	spin_unlock_irq(&crc->lock);
+
 	crtc->funcs->set_crc_source(crtc, NULL);
 
 	spin_lock_irq(&crc->lock);