spi: imx: Fix small DMA transfers

DMA transfers must be greater than the watermark level size. spi_imx->rx_wml
and spi_imx->tx_wml contain the watermark level in 32bit words whereas struct
spi_transfer contains the transfer len in bytes. Fix the check if DMA is
possible for a transfer accordingly. This fixes transfers with sizes between
33 and 128 bytes for which previously was claimed that DMA is possible.

Fixes: f62caccd12c17e4 (spi: spi-imx: add DMA support)
Signed-off-by: Sascha Hauer <s.hauer@pengutronix.de>
Cc: stable@vger.kernel.org
Signed-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-imx.c

@@ -201,8 +201,9 @@ static bool spi_imx_can_dma(struct spi_master *master, struct spi_device *spi,
 {
 	struct spi_imx_data *spi_imx = spi_master_get_devdata(master);
 
-	if (spi_imx->dma_is_inited && (transfer->len > spi_imx->rx_wml)
-	    && (transfer->len > spi_imx->tx_wml))
+	if (spi_imx->dma_is_inited
+	    && transfer->len > spi_imx->rx_wml * sizeof(u32)
+	    && transfer->len > spi_imx->tx_wml * sizeof(u32))
 		return true;
 	return false;
 }