net: stmmac: dwmac-generic: use stmmac_pltfr_exit()

Shrink the code in dwmac-generic by using the new stmmac_pltfr_exit()
helper.

Signed-off-by: Bartosz Golaszewski <bartosz.golaszewski@linaro.org>
Link: https://lore.kernel.org/r/20230623100417.93592-5-brgl@bgdev.pl
Signed-off-by: Jakub Kicinski <kuba@kernel.org>

Author: Bartosz Golaszewski

drivers/net/ethernet/stmicro/stmmac/dwmac-generic.c

@@ -58,8 +58,7 @@ static int dwmac_generic_probe(struct platform_device *pdev)
 	return 0;
 
 err_exit:
-	if (plat_dat->exit)
-		plat_dat->exit(pdev, plat_dat->bsp_priv);
+	stmmac_pltfr_exit(pdev, plat_dat);
 err_remove_config_dt:
 	if (pdev->dev.of_node)
 		stmmac_remove_config_dt(pdev, plat_dat);