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/net/sunrpc/cache.c b/net/sunrpc/cache.c
index 5e4f815..2b32fd6 100644
--- a/net/sunrpc/cache.c
+++ b/net/sunrpc/cache.c
@@ -771,7 +771,7 @@
 	if (count == 0)
 		return 0;
 
-	mutex_lock(&inode->i_mutex); /* protect against multiple concurrent
+	inode_lock(inode); /* protect against multiple concurrent
 			      * readers on this file */
  again:
 	spin_lock(&queue_lock);
@@ -784,7 +784,7 @@
 	}
 	if (rp->q.list.next == &cd->queue) {
 		spin_unlock(&queue_lock);
-		mutex_unlock(&inode->i_mutex);
+		inode_unlock(inode);
 		WARN_ON_ONCE(rp->offset);
 		return 0;
 	}
@@ -838,7 +838,7 @@
 	}
 	if (err == -EAGAIN)
 		goto again;
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 	return err ? err :  count;
 }
 
@@ -909,9 +909,9 @@
 	if (!cd->cache_parse)
 		goto out;
 
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 	ret = cache_downcall(mapping, buf, count, cd);
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 out:
 	return ret;
 }