ceph: make ceph_netfs_read_ops static

The sparse tool complains as follows:

fs/ceph/addr.c:316:37: warning:
 symbol 'ceph_netfs_read_ops' was not declared. Should it be static?

This symbol is not used outside of addr.c, so mark it static.
Reported-by: Hulk Robot <hulkci@huawei.com>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Reviewed-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>

fs/ceph/addr.c

@@ -305,7 +305,7 @@ static void ceph_readahead_cleanup(struct address_space *mapping, void *priv)
 		ceph_put_cap_refs(ci, got);
 }
 
-const struct netfs_read_request_ops ceph_netfs_read_ops = {
+static const struct netfs_read_request_ops ceph_netfs_read_ops = {
 	.init_rreq		= ceph_init_rreq,
 	.is_cache_enabled	= ceph_is_cache_enabled,
 	.begin_cache_operation	= ceph_begin_cache_operation,