slimbus: qcom: fix potential NULL dereference in qcom_slim_prg_slew()

platform_get_resource_byname() may fail and in this case a NULL
dereference will occur.

Fix it to use devm_platform_ioremap_resource_byname() instead of calling
platform_get_resource_byname() and devm_ioremap().

This is detected by Coccinelle semantic patch.

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

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

Fixes: ad7fcbc3

 ("slimbus: qcom: Add Qualcomm Slimbus controller driver")
Signed-off-by: Zhang Changzhong <zhangchangzhong@huawei.com>
Link: https://lore.kernel.org/r/1607392473-20610-1-git-send-email-zhangchangzhong@huawei.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>