power: supply: bq256xx: fix some problem in bq256xx_hw_init

smatch complains that there is a buffer overflow and clang complains
'ret' is never read.

Smatch error:
drivers/power/supply/bq256xx_charger.c:1578 bq256xx_hw_init() error:
buffer overflow 'bq256xx_watchdog_time' 4 <= 4

Clang static checker:
Value stored to 'ret' is never read.

Add check for buffer overflow and error code from regmap_update_bits().

Fixes: 32e4978 ("power: supply: bq256xx: Introduce the BQ256XX charger driver")
Signed-off-by: Su Hui <suhui@nfschina.com>
Link: https://lore.kernel.org/r/20231116041822.1378758-1-suhui@nfschina.com
Signed-off-by: Sebastian Reichel <sebastian.reichel@collabora.com>

drivers/power/supply/bq256xx_charger.c

@@ -1574,13 +1574,16 @@ static int bq256xx_hw_init(struct bq256xx_device *bq)
 			wd_reg_val = i;
 			break;
 		}
-		if (bq->watchdog_timer > bq256xx_watchdog_time[i] &&
+		if (i + 1 < BQ256XX_NUM_WD_VAL &&
+		    bq->watchdog_timer > bq256xx_watchdog_time[i] &&
 		    bq->watchdog_timer < bq256xx_watchdog_time[i + 1])
 			wd_reg_val = i;
 	}
 	ret = regmap_update_bits(bq->regmap, BQ256XX_CHARGER_CONTROL_1,
 				 BQ256XX_WATCHDOG_MASK, wd_reg_val <<
 						BQ256XX_WDT_BIT_SHIFT);
+	if (ret)
+		return ret;
 
 	ret = power_supply_get_battery_info(bq->charger, &bat_info);
 	if (ret == -ENOMEM)