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/read_write.c b/fs/read_write.c
index 06b07d5..fa05985 100644
--- a/fs/read_write.c
+++ b/fs/read_write.c
@@ -238,7 +238,7 @@
 	struct inode *inode = file_inode(file);
 	loff_t retval;
 
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 	switch (whence) {
 		case SEEK_END:
 			offset += i_size_read(inode);
@@ -283,7 +283,7 @@
 		retval = offset;
 	}
 out:
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 	return retval;
 }
 EXPORT_SYMBOL(default_llseek);