spi: omap2-mcspi: Disable multi mode when CS should be kept asserted after message

spi: omap2-mcspi: Disable multi mode when CS should be kept asserted after message

When the last transfer of a SPI message has the cs_change flag, the CS is kept
asserted after the message.
Multi-mode can't respect this as CS is deasserted by the hardware at the end of
the message.

Disable multi-mode when not applicable to the current message.

Fixes: d153ff4056cb ("spi: omap2-mcspi: Add support for MULTI-mode")
Signed-off-by: Félix Piédallu <felix.piedallu@non.se.com>
Link: https://patch.msgid.link/20250606-cs_change_fix-v1-1-27191a98a2e5@non.se.com
Signed-off-by: Mark Brown <broonie@kernel.org>