block: Use bdrv_reopen_set_read_only() in bdrv_backing_update_filename()

This patch replaces the bdrv_reopen() calls that set and remove the
BDRV_O_RDWR flag with the new bdrv_reopen_set_read_only() function.
Signed-off-by: NAlberto Garcia <berto@igalia.com>
Reviewed-by: NMax Reitz <mreitz@redhat.com>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -1079,11 +1079,11 @@ static int bdrv_backing_update_filename(BdrvChild *c, BlockDriverState *base,
                                         const char *filename, Error **errp)
 {
     BlockDriverState *parent = c->opaque;
-    int orig_flags = bdrv_get_flags(parent);
+    bool read_only = bdrv_is_read_only(parent);
     int ret;
 
-    if (!(orig_flags & BDRV_O_RDWR)) {
-        ret = bdrv_reopen(parent, orig_flags | BDRV_O_RDWR, errp);
+    if (read_only) {
+        ret = bdrv_reopen_set_read_only(parent, false, errp);
         if (ret < 0) {
             return ret;
         }
@@ -1095,8 +1095,8 @@ static int bdrv_backing_update_filename(BdrvChild *c, BlockDriverState *base,
         error_setg_errno(errp, -ret, "Could not update backing file link");
     }
 
-    if (!(orig_flags & BDRV_O_RDWR)) {
-        bdrv_reopen(parent, orig_flags, NULL);
+    if (read_only) {
+        bdrv_reopen_set_read_only(parent, true, NULL);
     }
 
     return ret;