spi: omap2-mcspi: Remove redundant checks

spi: omap2-mcspi: Remove redundant checks

Both omap2_mcspi_tx_dma() and omap2_mcspi_rx_dma() are only called from
omap2_mcspi_txrx_dma() and omap2_mcspi_txrx_dma() is always called after
making sure that mcspi_dma->dma_rx and mcspi_dma->dma_tx are not NULL
(see omap2_mcspi_transfer_one()).
Therefore remove redundant NULL checks for omap2_mcspi->dma_tx and
omap2_mcspi->dma_rx pointers in omap2_mcspi_tx_dma() and
omap2_mcspi_rx_dma() respectively.

Signed-off-by: Vignesh Raghavendra <vigneshr@ti.com>
Link: https://lore.kernel.org/r/20191109041827.26934-1-vigneshr@ti.com
Signed-off-by: Mark Brown <broonie@kernel.org>