gpu: drm: radeon: radeon_drv: Remove unused variable 'ret'

gpu: drm: radeon: radeon_drv: Remove unused variable 'ret'

Fixes the following W=1 kernel build warning(s):

 drivers/gpu/drm/radeon/radeon_drv.c: In function ‘radeon_pmops_runtime_suspend’:
 drivers/gpu/drm/radeon/radeon_drv.c:455:6: warning: variable ‘ret’ set but not used [-Wunused-but-set-variable]

Cc: Alex Deucher <alexander.deucher@amd.com>
Cc: "Christian König" <christian.koenig@amd.com>
Cc: David Airlie <airlied@linux.ie>
Cc: Daniel Vetter <daniel@ffwll.ch>
Cc: Gareth Hughes <gareth@valinux.com>
Cc: amd-gfx@lists.freedesktop.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>