[ARM] Orion: activate workaround for 88f6183 SPI clock erratum

Commit 2ede90ca78500ca0ffeee19d7812d345f8ad152d adds 6183 support,
but the SPI support in there doesn't work since it depends on a
6183 SPI unit erratum fix that only just went upstream, via commit
2bec19fe

.

Signed-off-by: Nicolas Pitre <nico@marvell.com>