wrappers for ->i_mutex access

parallel to mutex_{lock,unlock,trylock,is_locked,lock_nested},
inode_foo(inode) being mutex_foo(&inode->i_mutex).

Please, use those for access to ->i_mutex; over the coming cycle
->i_mutex will become rwsem, with ->lookup() done with it held
only shared.

Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>
diff --git a/fs/overlayfs/copy_up.c b/fs/overlayfs/copy_up.c
index eff6319..d894e7c 100644
--- a/fs/overlayfs/copy_up.c
+++ b/fs/overlayfs/copy_up.c
@@ -248,9 +248,9 @@
 	if (err)
 		goto out_cleanup;
 
-	mutex_lock(&newdentry->d_inode->i_mutex);
+	inode_lock(newdentry->d_inode);
 	err = ovl_set_attr(newdentry, stat);
-	mutex_unlock(&newdentry->d_inode->i_mutex);
+	inode_unlock(newdentry->d_inode);
 	if (err)
 		goto out_cleanup;