pinctrl: make pinctrl_register() return proper error code

Currently, pinctrl_register() just returns NULL on error, so the
callers can not know the exact reason of the failure.

Some of the pinctrl drivers return -EINVAL, some -ENODEV, and some
-ENOMEM on error of pinctrl_register(), although the error code
might be different from the real cause of the error.

This commit reworks pinctrl_register() to return the appropriate
error code and modifies all of the pinctrl drivers to use IS_ERR()
for the error checking and PTR_ERR() for getting the error code.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Acked-by: Patrice Chotard <patrice.chotard@st.com>
Acked-by: Thierry Reding <treding@nvidia.com>
Acked-by: Heiko Stuebner <heiko@sntech.de>
Tested-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Acked-by: Lee Jones <lee@kernel.org>
Acked-by: Sören Brinkmann <soren.brinkmann@xilinx.com>
Acked-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Acked-by: Ray Jui <rjui@broadcom.com>
Acked-by: Antoine Tenart <antoine.tenart@free-electrons.com>
Acked-by: Hongzhou Yang <hongzhou.yang@mediatek.com>
Acked-by: Wei Chen <Wei.Chen@csr.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/mediatek/pinctrl-mtk-common.c

@@ -1269,9 +1269,9 @@ int mtk_pctrl_init(struct platform_device *pdev,
 	mtk_pctrl_desc.npins = pctl->devdata->npins;
 	pctl->dev = &pdev->dev;
 	pctl->pctl_dev = pinctrl_register(&mtk_pctrl_desc, &pdev->dev, pctl);
-	if (!pctl->pctl_dev) {
+	if (IS_ERR(pctl->pctl_dev)) {
 		dev_err(&pdev->dev, "couldn't register pinctrl driver\n");
-		return -EINVAL;
+		return PTR_ERR(pctl->pctl_dev);
 	}
 
 	pctl->chip = devm_kzalloc(&pdev->dev, sizeof(*pctl->chip), GFP_KERNEL);