winsys/radeon: check null return from radeon_cs_create_fence in cs_flush

Follow-up of patch:
"radeon_cs_create_fence: check null return from radeon_winsys_bo_create"

radeon_drm_cs_flush
  radeon_cs_create_fence
    radeon_winsys_bo_create

Signed-off-by: Julien Isorce <jisorce@oblong.com>
Signed-off-by: Marek Olšák <marek.olsak@amd.com>
(cherry picked from commit d08c0930af8aaef5bdf80df618bb906e0b349830)
[Emil Velikov: resolve trivial conflicts]
Nominated-by: Emil Velikov <emil.velikov@collabora.com>
Signed-off-by: Emil Velikov <emil.velikov@collabora.com>

Conflicts:
	src/gallium/winsys/radeon/drm/radeon_drm_cs.c
1 file changed