docs:fix glBlitFramebuffer() for Gallium

docs/relnotes-7.5.1.html

@@ -47,6 +47,7 @@ tbd
 <li>Fixed front buffer rendering bug in Intel drivers.
 <li>Fixed minor GLX memory leaks.
 <li>Fixed some texture env / fragment program state bugs.
+<li>Fixed some Gallium glBlitFramebuffer() bugs
 </ul>