[spi_host] Fix bug around invalid direction detection.
[spi_host] Fix bug around invalid direction detection.

Dual and Qual mode transactions are invalid if the are bidirectional.
Previously this code flagged an error if such segments were anything
but bidirectional.

Bug first noted in #10680.

Signed-off-by: Martin Lueker-Boden <7e82c17fafb3b7b91b3c3396a2f21a060e5a6c3d@wdc.com>

lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan,lowRISC/opentitan