soc/amd/stoneyridge/southbridge: fix setting SPI_USE_SPI100

Use a read modify write sequence when setting the SPI_USE_SPI100 bit in
the SPI100_ENABLE register. This avoids clearing other bits in the
register which might cause instabilities of the SPI interface. The
reference code for Stoneyrige also only sets the SPI_USE_SPI100 bit and
doesn't zero out the other bits.

TEST=None

Signed-off-by: Felix Held <felix-coreboot@felixheld.de>
Change-Id: I4d32fc2084bb34ea57924bae68511c6836587790
Reviewed-on: https://review.coreboot.org/c/coreboot/+/59933
Tested-by: build bot (Jenkins) <no-reply@coreboot.org>
Reviewed-by: Marshall Dawson <marshalldawson3rd@gmail.com>

0 files changed, 0 insertions, 0 deletions