nvc0: free memory allocated by the prog which reads MP perf counters

This fixes a long time ago memory leak (even before all my query
related changes).

Signed-off-by: Samuel Pitoiset <samuel.pitoiset@gmail.com>
Reviewed-by: Ilia Mirkin <imirkin@alum.mit.edu>
Cc: "11.0 11.1" <mesa-stable@lists.freedesktop.org>

src/gallium/drivers/nouveau/nvc0/nvc0_screen.c

@@ -428,6 +428,7 @@ nvc0_screen_destroy(struct pipe_screen *pscreen)
    if (screen->pm.prog) {
       screen->pm.prog->code = NULL; /* hardcoded, don't FREE */
       nvc0_program_destroy(NULL, screen->pm.prog);
+      FREE(screen->pm.prog);
    }
 
    nouveau_bo_ref(NULL, &screen->text);