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/exofs/file.c b/fs/exofs/file.c
index 906de66..28645f0 100644
--- a/fs/exofs/file.c
+++ b/fs/exofs/file.c
@@ -52,9 +52,9 @@
 	if (ret)
 		return ret;
 
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 	ret = sync_inode_metadata(filp->f_mapping->host, 1);
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 	return ret;
 }