clk: hisilicon: hi3660：Fix potential NULL dereference in hi3660_stub_clk_probe()

platform_get_resource() may return NULL, add proper check to
avoid potential NULL dereferencing.

This is detected by Coccinelle semantic patch.

@@
expression pdev, res, n, t, e, e1, e2;
@@

res = platform_get_resource(pdev, t, n);
+ if (!res)
+   return -EINVAL;
... when != res == NULL
e = devm_ioremap(e1, res->start, e2);

Fixes: 4f16f7ff3bc0 ("clk: hisilicon: Add support for Hi3660 stub clocks")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Stephen Boyd <sboyd@kernel.org>

drivers/clk/hisilicon/clk-hi3660-stub.c

@@ -149,6 +149,8 @@ static int hi3660_stub_clk_probe(struct platform_device *pdev)
 		return PTR_ERR(stub_clk_chan.mbox);
 
 	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
+	if (!res)
+		return -EINVAL;
 	freq_reg = devm_ioremap(dev, res->start, resource_size(res));
 	if (!freq_reg)
 		return -ENOMEM;