Current DMA engine implementation of pxa2xx_spi_dma_prepare() don't use
the dma_burst argument. Remove it since it became unused after
commit 6356437e ("spi: spi-pxa2xx: remove legacy PXA DMA bits").
Signed-off-by: NJarkko Nikula <jarkko.nikula@linux.intel.com>
Signed-off-by: NMark Brown <broonie@kernel.org>