power: supply: max17042_battery: Prevent int underflow in set_soc_threshold

max17042_set_soc_threshold gets called with offset set to 1, which means
that minimum threshold value would underflow once SOC got down to 0,
causing invalid alerts from the gauge.

Fixes: e5f3872d ("max17042: Add support for signalling change in SOC")
Cc: <stable@vger.kernel.org>
Signed-off-by: Sebastian Krzyszkowiak <sebastian.krzyszkowiak@puri.sm>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@canonical.com>
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/max17042_battery.c

@@ -860,7 +860,8 @@ static void max17042_set_soc_threshold(struct max17042_chip *chip, u16 off)
 	regmap_read(map, MAX17042_RepSOC, &soc);
 	soc >>= 8;
 	soc_tr = (soc + off) << 8;
-	soc_tr |= (soc - off);
+	if (off < soc)
+		soc_tr |= soc - off;
 	regmap_write(map, MAX17042_SALRT_Th, soc_tr);
 }