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>

fs/ioctl.c

@@ -434,9 +434,9 @@ int generic_block_fiemap(struct inode *inode,
 			 u64 len, get_block_t *get_block)
 {
 	int ret;
-	mutex_lock(&inode->i_mutex);
+	inode_lock(inode);
 	ret = __generic_block_fiemap(inode, fieinfo, start, len, get_block);
-	mutex_unlock(&inode->i_mutex);
+	inode_unlock(inode);
 	return ret;
 }
 EXPORT_SYMBOL(generic_block_fiemap);