power: change from meaningless value to error number

'-1' is absolutely meaningless value.
This patch changed from meaningless value to error number.

Signed-off-by: Jaehoon Chung <jh80.chung@samsung.com>
Reviewed-by: Simon Glass <sjg@chromium.org>
diff --git a/drivers/power/battery/bat_trats2.c b/drivers/power/battery/bat_trats2.c
index 57221ad..6329e02 100644
--- a/drivers/power/battery/bat_trats2.c
+++ b/drivers/power/battery/bat_trats2.c
@@ -18,7 +18,7 @@
 	struct power_battery *p_bat = bat->pbat;
 
 	if (bat->chrg->chrg_state(p_bat->chrg, PMIC_CHARGER_ENABLE, 450))
-		return -1;
+		return -EINVAL;
 
 	return 0;
 }