XArray: Optimise xas_sibling() if !CONFIG_XARRAY_MULTI

If CONFIG_XARRAY_MULTI is disabled, then xas_sibling() must be false.
Reported-by: JaeJoon Jung <rgbi3307@gmail.com>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>

lib/xarray.c

@@ -1836,7 +1836,7 @@ static bool xas_sibling(struct xa_state *xas)
 	struct xa_node *node = xas->xa_node;
 	unsigned long mask;
 
-	if (!node)
+	if (!IS_ENABLED(CONFIG_XARRAY_MULTI) || !node)
 		return false;
 	mask = (XA_CHUNK_SIZE << node->shift) - 1;
 	return (xas->xa_index & mask) >