MIPS: ralink: fix return value check in rt_timer_probe()

In case of error, the function devm_request_and_ioremap() returns NULL
pointer not ERR_PTR(). Fix it by using devm_ioremap_resource() instead
of devm_request_and_ioremap().
Signed-off-by: Wei Yongjun <yongjun_wei@trendmicro.com.cn>
Acked-by: John Crispin <blogic@openwrt.org>
Cc: grant.likely@linaro.org
Cc: rob.herring@calxeda.com
Cc: linux-mips@linux-mips.org
Patchwork: https://patchwork.linux-mips.org/patch/6098/Signed-off-by: Ralf Baechle <ralf@linux-mips.org>

arch/mips/ralink/timer.c

@@ -126,7 +126,7 @@ static int rt_timer_probe(struct platform_device *pdev)
 		return -ENOENT;
 	}
 
-	rt->membase = devm_request_and_ioremap(&pdev->dev, res);
+	rt->membase = devm_ioremap_resource(&pdev->dev, res);
 	if (IS_ERR(rt->membase))
 		return PTR_ERR(rt->membase);