This adds GRAPH_RDLOCK annotations to declare that callers of
bdrv_child_perm() need to hold a reader lock for the graph because
some implementations access the children list of a node.

The callers of bdrv_child_perm() conveniently already hold the lock.

Signed-off-by: Kevin Wolf <kwolf@redhat.com>
Reviewed-by: Emanuele Giuseppe Esposito <eesposit@redhat.com>
Reviewed-by: Stefan Hajnoczi <stefanha@redhat.com>
Message-ID: <20230911094620.45040-16-kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>