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/mfd/fg_max77693.c b/drivers/power/mfd/fg_max77693.c
index 4519fed..df15508 100644
--- a/drivers/power/mfd/fg_max77693.c
+++ b/drivers/power/mfd/fg_max77693.c
@@ -52,7 +52,7 @@
 
 	if (pmic_probe(p)) {
 		puts("Can't find max77693 fuel gauge\n");
-		return -1;
+		return -ENODEV;
 	}
 
 	ret = max77693_get_soc(&pb->bat->state_of_chrg);
@@ -74,7 +74,7 @@
 
 	if (pmic_probe(p)) {
 		puts("Can't find max77693 fuel gauge\n");
-		return -1;
+		return -ENODEV;
 	}
 
 	ret = pmic_reg_read(p, MAX77693_STATUS, &val);