doc: Fix xref in functions description

This was accidentally broken by 3c78ad2561.

doc/functions/library/attrsets.xml

@@ -166,7 +166,7 @@ lib.attrsets.setAttrByPath [ "a" "b" ] 3
   <xi:include href="./locations.xml" xpointer="lib.attrsets.getAttrFromPath" />
 
   <para>
-   Like [](#function-library-lib.attrsets.attrByPath) except without a default, and it will throw if the value doesn't exist.
+   Like <xref linkend="function-library-lib.attrsets.attrByPath" /> except without a default, and it will throw if the value doesn't exist.
   </para>
 
   <variablelist>
@@ -1480,7 +1480,7 @@ lib.attrsets.zipAttrsWith
   <xi:include href="./locations.xml" xpointer="lib.attrsets.zipAttrs" />
 
   <para>
-   Merge sets of attributes and combine each attribute value in to a list. Similar to [](#function-library-lib.attrsets.zipAttrsWith) where the merge function returns a list of all values.
+   Merge sets of attributes and combine each attribute value in to a list. Similar to <xref linkend="function-library-lib.attrsets.zipAttrsWith" /> where the merge function returns a list of all values.
   </para>
 
   <variablelist>