Bug fix to correct return value of gxp_spi_write function to zero.
Completion of succesful operation should return zero.

Fixes: 730bc8ba spi: spi-gxp: Add support for HPE GXP SoCs
Signed-off-by: Charles Kearney <charles.kearney@hpe.com>
Link: https://lore.kernel.org/r/20230920215339.4125856-2-charles.kearney@hpe.comSigned-off-by: Mark Brown <broonie@kernel.org>