pinctrl: realtek: Fix some NULL dereference warnings

Just inspecting the code doesn't convince me that this is a real
issue, but the tools complain that it is so I will just handle it.

Cc: Tzuyi Chang <tychang@realtek.com>
Link: https://lore.kernel.org/oe-kbuild-all/202309270234.aJGlDE0P-lkp@intel.com/
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
Link: https://lore.kernel.org/r/20231006-fix-realtek-warnings-v1-2-09af253312ba@linaro.org

Author: Linus Walleij

drivers/pinctrl/realtek/pinctrl-rtd.c

@@ -165,7 +165,10 @@ static int rtd_pinctrl_set_one_mux(struct pinctrl_dev *pcdev,
 		return 0;
 
 	if (!mux->functions) {
-		dev_err(pcdev->dev, "No functions available for pin %s\n", mux->name);
+		if (!mux->name)
+			dev_err(pcdev->dev, "NULL pin has no functions\n");
+		else
+			dev_err(pcdev->dev, "No functions available for pin %s\n", mux->name);
 		return -ENOTSUPP;
 	}
 
@@ -177,6 +180,11 @@ static int rtd_pinctrl_set_one_mux(struct pinctrl_dev *pcdev,
 		return ret;
 	}
 
+	if (!mux->name) {
+		dev_err(pcdev->dev, "NULL pin provided for function %s\n", func_name);
+		return -EINVAL;
+	}
+
 	dev_err(pcdev->dev, "No function %s available for pin %s\n", func_name, mux->name);
 
 	return -EINVAL;