platform/x86: hp-wmi: Refactor postcode_store() to follow standard patterns

Refactor postcode_store() to follow standard patterns of error handling.

While at it, switch to use kstrtobool().
Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>

drivers/platform/x86/hp-wmi.c

@@ -473,22 +473,20 @@ static ssize_t als_store(struct device *dev, struct device_attribute *attr,
 static ssize_t postcode_store(struct device *dev, struct device_attribute *attr,
 			      const char *buf, size_t count)
 {
-	long unsigned int tmp2;
+	u32 tmp = 1;
+	bool clear;
 	int ret;
-	u32 tmp;
 
-	ret = kstrtoul(buf, 10, &tmp2);
-	if (!ret && tmp2 != 1)
-		ret = -EINVAL;
+	ret = kstrtobool(buf, &clear);
 	if (ret)
-		goto out;
+		return ret;
+
+	if (clear == false)
+		return -EINVAL;
 
 	/* Clear the POST error code. It is kept until until cleared. */
-	tmp = (u32) tmp2;
 	ret = hp_wmi_perform_query(HPWMI_POSTCODEERROR_QUERY, HPWMI_WRITE, &tmp,
 				       sizeof(tmp), sizeof(tmp));
-
-out:
 	if (ret)
 		return ret < 0 ? ret : -EINVAL;