spi: Fix regression in spi-bitbang-txrx.h

spi: Fix regression in spi-bitbang-txrx.h

commit 26a67ec47a4c58fe79c6421c3dc3d697d322d2d6 upstream.

This patch fixes a regression introduced by commit 232a5adc5199 ("spi:
bitbang: only toggle bitchanges"). The attempt to optimize writes of
consecutive bit patterns broke most of the combinations of word size
and SPI modes due to selecting the wrong bit as the MSB value.

Fixes: 232a5adc5199 (spi: bitbang: only toggle bitchanges)
Signed-off-by: Lars Persson <larper@axis.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>