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/axp152.c b/drivers/power/axp152.c
index cd07275..c4b3fe5 100644
--- a/drivers/power/axp152.c
+++ b/drivers/power/axp152.c
@@ -75,7 +75,7 @@
 		return rc;
 
 	if (ver != 0x05)
-		return -1;
+		return -EINVAL;
 
 	return 0;
 }