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>

drivers/usb/gadget/legacy/inode.c

@@ -1521,10 +1521,10 @@ static void destroy_ep_files (struct dev_data *dev)
 		spin_unlock_irq (&dev->lock);
 
 		/* break link to dcache */
-		mutex_lock (&parent->i_mutex);
+		inode_lock(parent);
 		d_delete (dentry);
 		dput (dentry);
-		mutex_unlock (&parent->i_mutex);
+		inode_unlock(parent);
 
 		spin_lock_irq (&dev->lock);
 	}