drm/radeon: fix regression in UMS CS ioctl

radeon_cs_parser_init is called by both the legacy UMS
CS ioctl and the KMS CS ioctl.  Protect KMS specific
pieces of the code by checking that rdev is not NULL.
Reported-by: Michael Burian <michael.burian@sbg.at>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Reviewed-by: Jerome Glisse <jglisse@redhat.com>
Cc: stable@vger.kernel.org
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_cs.c

@@ -147,6 +147,7 @@ static int radeon_cs_sync_rings(struct radeon_cs_parser *p)
 					   sync_to_ring, p->ring);
 }
 
+/* XXX: note that this is called from the legacy UMS CS ioctl as well */
 int radeon_cs_parser_init(struct radeon_cs_parser *p, void *data)
 {
 	struct drm_radeon_cs *cs = data;
@@ -245,6 +246,8 @@ int radeon_cs_parser_init(struct radeon_cs_parser *p, void *data)
 		}
 	}
 
+	/* these are KMS only */
+	if (p->rdev) {
 		if ((p->cs_flags & RADEON_CS_USE_VM) &&
 		    !p->rdev->vm_manager.enabled) {
 			DRM_ERROR("VM not active on asic!\n");
@@ -260,7 +263,7 @@ int radeon_cs_parser_init(struct radeon_cs_parser *p, void *data)
 
 		if (radeon_cs_get_ring(p, ring, priority))
 			return -EINVAL;
-
+	}
 
 	/* deal with non-vm */
 	if ((p->chunk_ib_idx != -1) &&