drm/radeon: check for allocation failure in radeon_ring_backup()

Static checkers complain if this we don't check for allocation failure.
Also we can use the new kmalloc_array() function here as a cleanup.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Dave Airlie <airlied@redhat.com>

drivers/gpu/drm/radeon/radeon_ring.c

@@ -594,7 +594,11 @@ unsigned radeon_ring_backup(struct radeon_device *rdev, struct radeon_ring *ring
 	}
 
 	/* and then save the content of the ring */
-	*data = kmalloc(size * 4, GFP_KERNEL);
+	*data = kmalloc_array(size, sizeof(uint32_t), GFP_KERNEL);
+	if (!*data) {
+		mutex_unlock(&rdev->ring_lock);
+		return 0;
+	}
 	for (i = 0; i < size; ++i) {
 		(*data)[i] = ring->ring[ptr++];
 		ptr &= ring->ptr_mask;