The GPI DMA mode requires for TX DMA to be prepared. Force SPI core to
provide TX buffer even if the caller didn't provide one by setting the
SPI_CONTROLLER_MUST_TX flag.

Fixes: b59c1224 ("spi: spi-geni-qcom: Add support for GPI dma")
Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
Link: https://lore.kernel.org/r/20230629095847.3648597-1-dmitry.baryshkov@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>