glGetnHistogram: Added len to param values to match glGetnHistogramARB

xml/gl.xml

diff --git a/xml/gl.xml b/xml/gl.xml
index 89e39d0..186f3c9 100644
--- a/xml/gl.xml
+++ b/xml/gl.xml
@@ -20722,7 +20722,7 @@
             <param group="PixelFormat"><ptype>GLenum</ptype> <name>format</name></param>
             <param group="PixelType"><ptype>GLenum</ptype> <name>type</name></param>
             <param><ptype>GLsizei</ptype> <name>bufSize</name></param>
-            <param>void *<name>values</name></param>
+            <param len="bufSize">void *<name>values</name></param>
         </command>
         <command>
             <proto>void <name>glGetnHistogramARB</name></proto>