drm: fixup improper cast.

Signed-off-by: Dave Airlie <airlied@linux.ie>
diff --git a/drivers/char/drm/radeon_state.c b/drivers/char/drm/radeon_state.c
index 56e56b8..b006b1c 100644
--- a/drivers/char/drm/radeon_state.c
+++ b/drivers/char/drm/radeon_state.c
@@ -1996,7 +1996,7 @@
 		return DRM_ERR(EINVAL);
 	}
 
-	DRM_COPY_FROM_USER_IOCTL(memfree, (drm_radeon_mem_free_t __user *) data,
+	DRM_COPY_FROM_USER_IOCTL(memfree, (drm_radeon_surface_free_t __user *) data,
 				 sizeof(memfree));
 
 	if (free_surface(filp, dev_priv, memfree.address))