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>

fs/ext4/namei.c

@@ -2753,7 +2753,7 @@ int ext4_orphan_add(handle_t *handle, struct inode *inode)
 		return 0;
 
 	WARN_ON_ONCE(!(inode->i_state & (I_NEW | I_FREEING)) &&
-		     !mutex_is_locked(&inode->i_mutex));
+		     !inode_is_locked(inode));
 	/*
 	 * Exit early if inode already is on orphan list. This is a big speedup
 	 * since we don't have to contend on the global s_orphan_lock.
@@ -2835,7 +2835,7 @@ int ext4_orphan_del(handle_t *handle, struct inode *inode)
 		return 0;
 
 	WARN_ON_ONCE(!(inode->i_state & (I_NEW | I_FREEING)) &&
-		     !mutex_is_locked(&inode->i_mutex));
+		     !inode_is_locked(inode));
 	/* Do this quick check before taking global s_orphan_lock. */
 	if (list_empty(&ei->i_orphan))
 		return 0;