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