spi: fsl-dspi: Avoid using -EINPROGRESS error code

spi: fsl-dspi: Avoid using -EINPROGRESS error code

Refactor dspi_rxtx() and dspi_poll() to not return -EINPROGRESS because
this isn't actually a status that is ever returned to the core layer but
some internal state. Use true/false return value on dspi_rxtx() for this
instead.

This will help separate internal vs external status for the later change
to store the external status directly in cur_msg->status.

No functional changes intended.

Co-developed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Signed-off-by: James Clark <james.clark@linaro.org>
Reviewed-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Message-ID: <20250902-james-nxp-spi-dma-v6-1-f7aa2c5e56e2@linaro.org>
Signed-off-by: Mark Brown <broonie@kernel.org>