egl_dri2: Zero out driver struct

Otherwise testing ->Probe for non-NULL and calling it goes boom.

src/egl/drivers/dri2/egl_dri2.c

@@ -1396,6 +1396,7 @@ _eglMain(const char *args)
    if (!dri2_drv)
       return NULL;
 
+   memset(dri2_drv, 0, sizeof *dri2_drv);
    _eglInitDriverFallbacks(&dri2_drv->base);
    dri2_drv->base.API.Initialize = dri2_initialize;
    dri2_drv->base.API.Terminate = dri2_terminate;