drm/amd/display: remove gcc warning Wunused-but-set-variable

drivers/gpu/drm/amd/display/dc/dce/dce_aux.c: In function dce_aux_configure_timeout:
drivers/gpu/drm/amd/display/dc/dce/dce_aux.c: warning: variable timeout set but not used [-Wunused-but-set-variable]

Signed-off-by: Chenwandun <chenwandun@huawei.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>