spi: Set ctlr->cur_msg also in the sync transfer case

Some drivers rely on this to point to the currently processed message, so
set this here also.

Signed-off-by: David Jander <david@protonic.nl>
Link: https://lore.kernel.org/r/20220621061234.3626638-10-david@protonic.nl


Signed-off-by: Mark Brown <broonie@kernel.org>