platform/x86: huawei-wmi: do not hard-code sizes

Use `sizeof()` and `ARRAY_SIZE()` instead of
hard-coding buffer sizes and indices.
Signed-off-by: Barnabás Pőcze <pobrn@protonmail.com>
Link: https://lore.kernel.org/r/20221005150032.173198-1-pobrn@protonmail.comReviewed-by: Hans de Goede <hdegoede@redhat.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>

drivers/platform/x86/huawei-wmi.c

@@ -323,12 +323,12 @@ static int huawei_wmi_battery_get(int *start, int *end)
 	u8 ret[0x100];
 	int err, i;
 
-	err = huawei_wmi_cmd(BATTERY_THRESH_GET, ret, 0x100);
+	err = huawei_wmi_cmd(BATTERY_THRESH_GET, ret, sizeof(ret));
 	if (err)
 		return err;
 
 	/* Find the last two non-zero values. Return status is ignored. */
-	i = 0xff;
+	i = ARRAY_SIZE(ret) - 1;
 	do {
 		if (start)
 			*start = ret[i-1];