spi: amd: Drop superfluous member from struct amd_spi

spi: amd: Drop superfluous member from struct amd_spi

The AMD SPI driver stores a pointer to the spi_master in struct amd_spi
so that it can get from the latter to the former in amd_spi_fifo_xfer().

It's simpler to just pass the pointer from the sole caller
amd_spi_master_transfer() and drop the pointer from struct amd_spi.

Signed-off-by: Lukas Wunner <lukas@wunner.de>
Link: https://lore.kernel.org/r/a088b684ad292faf3bd036e51529e608e5c94638.1588590210.git.lukas@wunner.de
Signed-off-by: Mark Brown <broonie@kernel.org>