i965: Free brw, not intel.

Things worked out in the past because both brw and intel share the same
memory address (by virtue of intel being the first member of brw).

However, brw is what actually gets rzalloc'd (brw_context.c:285), so
freeing that seems safer and more obvious.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Acked-by: Chris Forbes <chrisf@ijw.co.nz>
Acked-by: Paul Berry <stereotype441@gmail.com>
Acked-by: Anuj Phogat <anuj.phogat@gmail.com>

src/mesa/drivers/dri/i965/intel_context.c

@@ -639,7 +639,7 @@ intelDestroyContext(__DRIcontext * driContextPriv)
       /* free the Mesa context */
       _mesa_free_context_data(&intel->ctx);
 
-      ralloc_free(intel);
+      ralloc_free(brw);
       driContextPriv->driverPrivate = NULL;
    }
 }