nilfs2_permission() doesn't need to bail out in RCU mode

Nothing blocking except for generic_permission().  Which will DTRT.
Signed-off-by: NAl Viro <viro@zeniv.linux.org.uk>

fs/nilfs2/inode.c

@@ -801,12 +801,7 @@ int nilfs_setattr(struct dentry *dentry, struct iattr *iattr)
 
 int nilfs_permission(struct inode *inode, int mask, unsigned int flags)
 {
-	struct nilfs_root *root;
-
-	if (flags & IPERM_FLAG_RCU)
-		return -ECHILD;
-
-	root = NILFS_I(inode)->i_root;
+	struct nilfs_root *root = NILFS_I(inode)->i_root;
 	if ((mask & MAY_WRITE) && root &&
 	    root->cno != NILFS_CPTREE_CURRENT_CNO)
 		return -EROFS; /* snapshot is not writable */