drivers: fuel_gauge: remove dead code in set_prop functions

Remove useless assignments to `val` parameter in sbs_gauge_set_prop()
and bq27z746_set_prop(). Since `val` is passed by value, modifying it
has no effect. Also remove unused `tmp_val` variable.

Signed-off-by: Benjamin Cabé <benjamin@zephyrproject.org>

Author: kartben

drivers/fuel_gauge/bq27z746/bq27z746.c

@@ -241,16 +241,13 @@ static int bq27z746_set_prop(const struct device *dev, fuel_gauge_prop_t prop,
 			     union fuel_gauge_prop_val val)
 {
 	int rc = 0;
-	uint16_t tmp_val = 0;
 
 	switch (prop) {
 	case FUEL_GAUGE_SBS_MFR_ACCESS:
 		rc = bq27z746_write16(dev, BQ27Z746_MANUFACTURERACCESS, val.sbs_mfr_access_word);
-		val.sbs_mfr_access_word = tmp_val;
 		break;
 	case FUEL_GAUGE_SBS_ATRATE:
 		rc = bq27z746_write16(dev, BQ27Z746_ATRATE, val.sbs_at_rate);
-		val.sbs_at_rate = tmp_val;
 		break;
 	default:
 		rc = -ENOTSUP;

drivers/fuel_gauge/sbs_gauge/sbs_gauge.c

@@ -215,32 +215,26 @@ static int sbs_gauge_set_prop(const struct device *dev, fuel_gauge_prop_t prop,
 			      union fuel_gauge_prop_val val)
 {
 	int rc = 0;
-	uint16_t tmp_val = 0;
 
 	switch (prop) {
 
 	case FUEL_GAUGE_SBS_MFR_ACCESS:
 		rc = sbs_cmd_reg_write(dev, SBS_GAUGE_CMD_MANUFACTURER_ACCESS,
 				       val.sbs_mfr_access_word);
-		val.sbs_mfr_access_word = tmp_val;
 		break;
 	case FUEL_GAUGE_SBS_REMAINING_CAPACITY_ALARM:
 		rc = sbs_cmd_reg_write(dev, SBS_GAUGE_CMD_REM_CAPACITY_ALARM,
 				       val.sbs_remaining_capacity_alarm);
-		val.sbs_remaining_capacity_alarm = tmp_val;
 		break;
 	case FUEL_GAUGE_SBS_REMAINING_TIME_ALARM:
 		rc = sbs_cmd_reg_write(dev, SBS_GAUGE_CMD_REM_TIME_ALARM,
 				       val.sbs_remaining_time_alarm);
-		val.sbs_remaining_time_alarm = tmp_val;
 		break;
 	case FUEL_GAUGE_SBS_MODE:
 		rc = sbs_cmd_reg_write(dev, SBS_GAUGE_CMD_BATTERY_MODE, val.sbs_mode);
-		val.sbs_mode = tmp_val;
 		break;
 	case FUEL_GAUGE_SBS_ATRATE:
 		rc = sbs_cmd_reg_write(dev, SBS_GAUGE_CMD_AR, val.sbs_at_rate);
-		val.sbs_at_rate = tmp_val;
 		break;
 	default:
 		rc = -ENOTSUP;