eglfs-viv: Fix config test

fbGetDisplay() expects a context pointer, but the config test was
calling this function without any arguments, causing the test to
fail even when the Vivante EGLFS device integration is actually
supported.

This got broken in 5.7 by the INTEGRITY changes in
9b35b0e8dc6069aed563d0aca61c973eb307d772.

Task-number: QTBUG-53282
Change-Id: I233d93618b1c8a31d12b31139d3bfbd3d6429839
Done-with: Carlos Rafael Giani <dv@pseudoterminal.org>
Reviewed-by: Andy Nichols <andy.nichols@qt.io>

config.tests/qpa/eglfs-viv/eglfs-viv.cpp

@@ -43,6 +43,8 @@
 
 int main(int, char **)
 {
-    fbGetDisplay();
+    // Do not rely on fbGetDisplay() since the signature has changed over time.
+    // Stick to fbGetDisplayByIndex().
+    fbGetDisplayByIndex(0);
     return 0;
 }