pinctrl: add checks for empty function names

This is needed as otherwise we can get the following when
dealing with buggy data in a pinmux driver for
pinmux_search_function:

Unable to handle kernel NULL pointer dereference at virtual
address 00000000
...
PC is at strcmp+0xc/0x34
LR is at pinmux_get+0x350/0x8f4
...

As we need pctldev initialized to call ops->list_functions,
let's initialize it before check_ops calls and pass the
pctldev to the check_ops functions. Do this for both pinmux
and pinconf check_ops functions.

Signed-off-by: Tony Lindgren <tony@atomide.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>
diff --git a/drivers/pinctrl/pinconf.c b/drivers/pinctrl/pinconf.c
index 1892a37..9fb7545 100644
--- a/drivers/pinctrl/pinconf.c
+++ b/drivers/pinctrl/pinconf.c
@@ -205,8 +205,10 @@
 }
 EXPORT_SYMBOL(pin_config_group_set);
 
-int pinconf_check_ops(const struct pinconf_ops *ops)
+int pinconf_check_ops(struct pinctrl_dev *pctldev)
 {
+	const struct pinconf_ops *ops = pctldev->desc->confops;
+
 	/* We must be able to read out pin status */
 	if (!ops->pin_config_get && !ops->pin_config_group_get)
 		return -EINVAL;