drm/amd/display: Fix bug in debugfs crc_win_update entry

drm/amd/display: Fix bug in debugfs crc_win_update entry

[Why]
crc_rd_wrk shouldn't be null in crc_win_update_set(). Current programming
logic is inconsistent in crc_win_update_set().

[How]
Initially, return if crc_rd_wrk is NULL. Later on, we can use member of
crc_rd_wrk safely.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: eda37bc86d4a ("drm/amd/display: Use PSP TA to read out crc")
Reviewed-by: Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>
Acked-by: Pavle Kotarac <Pavle.Kotarac@amd.com>
Signed-off-by: Wayne Lin <Wayne.Lin@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>