spi: amd: Pass probe errors back to driver core

If probing fails, the AMD SPI driver pretends success to the driver core
by returning 0.  Return the errno instead.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/689f29a359718dab4f5de9ee66c02ea97b3bd9e8.1588590210.git.lukas@wunner.de


Signed-off-by: Mark Brown <broonie@kernel.org>