9p: don't allow delegations to be set on directories

With the advent of directory leases, it's necessary to set the
->setlease() handler in directory file_operations to properly deny them.

Fixes: e6d28ebc17eb ("filelock: push the S_ISREG check down to ->setlease handlers")
Signed-off-by: Jeff Layton <[e-mail]>
Link: https://patch.msgid.link/[e-mail]
Signed-off-by: Christian Brauner <[e-mail]>

fs/9p/vfs_dir.c

···
 	.iterate_shared = v9fs_dir_readdir,
 	.open = v9fs_file_open,
 	.release = v9fs_dir_release,
+	.setlease = simple_nosetlease,
 };
 
 const struct file_operations v9fs_dir_operations_dotl = {
···
 	.open = v9fs_file_open,
 	.release = v9fs_dir_release,
 	.fsync = v9fs_file_fsync_dotl,
+	.setlease = simple_nosetlease,
 };