spi: fsl-espi: remove element actual_length from struct fsl_espi_trans

If an error occurs during processing the message, then we don't have
to populate the actual_length element of struct message.
So we can get rid of element actual_length in struct
fsl_espi_transfer.

Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>