pinctrl: intel: merrifield: Add missed check in mrfld_config_set()

Not every pin can be configured. Add missed check to prevent access
violation.

Fixes: 4e80c8f505 ("pinctrl: intel: Add Intel Merrifield pin controller support")
Acked-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>

drivers/pinctrl/intel/pinctrl-merrifield.c

@@ -794,6 +794,9 @@ static int mrfld_config_set(struct pinctrl_dev *pctldev, unsigned int pin,
 	unsigned int i;
 	int ret;
 
+	if (!mrfld_buf_available(mp, pin))
+		return -ENOTSUPP;
+
 	for (i = 0; i < nconfigs; i++) {
 		switch (pinconf_to_config_param(configs[i])) {
 		case PIN_CONFIG_BIAS_DISABLE: