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/ubifs/file.c

@@ -1317,7 +1317,7 @@ int ubifs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	err = filemap_write_and_wait_range(inode->i_mapping, start, end);
 	if (err)
 		return err;
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 
 	/* Synchronize the inode unless this is a 'datasync()' call. */
 	if (!datasync || (inode->i_state & I_DIRTY_DATASYNC)) {
@@ -1332,7 +1332,7 @@ int ubifs_fsync(struct file *file, loff_t start, loff_t end, int datasync)
 	 */
 	err = ubifs_sync_wbufs_by_inode(c, inode);
 out:
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 	return err;
 }