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/coda/dir.c b/fs/coda/dir.c
index fda9f43..42e731b 100644
--- a/fs/coda/dir.c
+++ b/fs/coda/dir.c
@@ -427,13 +427,13 @@
 	if (host_file->f_op->iterate) {
 		struct inode *host_inode = file_inode(host_file);
 
-		mutex_lock(&host_inode->i_mutex);
+		inode_lock(host_inode);
 		ret = -ENOENT;
 		if (!IS_DEADDIR(host_inode)) {
 			ret = host_file->f_op->iterate(host_file, ctx);
 			file_accessed(host_file);
 		}
-		mutex_unlock(&host_inode->i_mutex);
+		inode_unlock(host_inode);
 		return ret;
 	}
 	/* Venus: we must read Venus dirents from a file */