master_xfer should return the number of messages successfully
processed.

Fixes: 0d676a6c ("i2c: add support for Socionext SynQuacer I2C controller")
Cc: <stable@vger.kernel.org> # v4.19+
Signed-off-by: Okamoto Satoru <okamoto.satoru@socionext.com>
Signed-off-by: Masahisa Kojima <masahisa.kojima@linaro.org>
Acked-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>