ds2782_battery: Fix signedness bug in ds278x_read_reg16()

We need to check for negative values before doing the swab16() for the
error handling to work.

Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Anton Vorontsov <anton.vorontsov@linaro.org>
diff --git a/drivers/power/ds2782_battery.c b/drivers/power/ds2782_battery.c
index 6bb6e2f..2fa9b6b 100644
--- a/drivers/power/ds2782_battery.c
+++ b/drivers/power/ds2782_battery.c
@@ -80,13 +80,13 @@
 {
 	int ret;
 
-	ret = swab16(i2c_smbus_read_word_data(info->client, reg_msb));
+	ret = i2c_smbus_read_word_data(info->client, reg_msb);
 	if (ret < 0) {
 		dev_err(&info->client->dev, "register read failed\n");
 		return ret;
 	}
 
-	*val = ret;
+	*val = swab16(ret);
 	return 0;
 }