spi: fsl: invert spisel_boot signal on MPC8309

spi: fsl: invert spisel_boot signal on MPC8309

Commit 7a2da5d7960a ("spi: fsl: Fix driver breakage when SPI_CS_HIGH
is not set in spi->mode") broke our MPC8309 board by effectively
inverting the boolean value passed to fsl_spi_cs_control. The
SPISEL_BOOT signal is used as chipselect, but it's not a gpio, so
we cannot rely on gpiolib handling the polarity.

Adapt to the new world order by inverting the logic here. This does
assume that the slave sitting at the SPISEL_BOOT is active low, but
should that ever turn out not to be the case, one can create a stub
gpiochip driver controlling a single gpio (or rather, a single "spo",
special-purpose output).

Fixes: 7a2da5d7960a ("spi: fsl: Fix driver breakage when SPI_CS_HIGH is not set in spi->mode")
Cc: stable@vger.kernel.org
Signed-off-by: Rasmus Villemoes <rasmus.villemoes@prevas.dk>
Link: https://lore.kernel.org/r/20210130143545.505613-1-rasmus.villemoes@prevas.dk
Signed-off-by: Mark Brown <broonie@kernel.org>