spi: spi-gxp: BUG: Correct spi write return value

spi: spi-gxp: BUG: Correct spi write return value

[ Upstream commit 1a8196a93e493c0a50b800cb09cef60b124eee15 ]

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

Fixes: 730bc8ba5e9e 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.com
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Sasha Levin <sashal@kernel.org>