rtc: ds1307: fix ds1307_native_smbus_read_block_data function

The i2c_smbus_read_i2c_block_data function returns 0 on success, not the
number of bytes written.

Hence, when there are 32 bytes or less to send, the
ds1307_native_smbus_write_block_data function returns 0 on success,
while it returns the number of bytes when there are more than 32.

The ds1307_write_block_data always returns the number of bytes on
success.
Signed-off-by: Nicolas Boullis <nboullis@debian.org>
Signed-off-by: Alexandre Belloni <alexandre.belloni@free-electrons.com>

drivers/rtc/rtc-ds1307.c

@@ -275,9 +275,13 @@ static s32 ds1307_native_smbus_write_block_data(const struct i2c_client *client,
 {
 	u8 suboffset = 0;
 
-	if (length <= I2C_SMBUS_BLOCK_MAX)
-		return i2c_smbus_write_i2c_block_data(client,
+	if (length <= I2C_SMBUS_BLOCK_MAX) {
+		s32 retval = i2c_smbus_write_i2c_block_data(client,
 					command, length, values);
+		if (retval < 0)
+			return retval;
+		return length;
+	}
 
 	while (suboffset < length) {
 		s32 retval = i2c_smbus_write_i2c_block_data(client,