drm/omap: accept NULL for dma_addr in omap_gem_pin

Allow NULL to be passed in 'dma_addr' for omap_gem_pin(), in case the
caller does not need the dma_addr.
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
Reviewed-by: Jean-Jacques Hiblot <jjhiblot@ti.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191010120000.1421-4-jjhiblot@ti.com

drivers/gpu/drm/omapdrm/omap_gem.c

@@ -819,9 +819,11 @@ int omap_gem_pin(struct drm_gem_object *obj, dma_addr_t *dma_addr)
 			refcount_inc(&omap_obj->dma_addr_cnt);
 		}
 
-		*dma_addr = omap_obj->dma_addr;
+		if (dma_addr)
+			*dma_addr = omap_obj->dma_addr;
 	} else if (omap_gem_is_contiguous(omap_obj)) {
-		*dma_addr = omap_obj->dma_addr;
+		if (dma_addr)
+			*dma_addr = omap_obj->dma_addr;
 	} else {
 		ret = -EINVAL;
 		goto fail;