spi: spi-fsl-dspi: Remove unused chip->void_write_data

This variable has been present since the initial submission of the
driver, and held, for some reason, the value of zero, to be sent on the
wire in the case there wasn't any TX buffer for the current transfer.

Since quite a while now, however, it isn't doing anything at all.
Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Link: https://lore.kernel.org/r/20200304220044.11193-3-olteanv@gmail.comSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-fsl-dspi.c

@@ -110,7 +110,6 @@
 
 struct chip_data {
 	u32			ctar_val;
-	u16			void_write_data;
 };
 
 enum dspi_trans_mode {
@@ -235,7 +234,6 @@ struct fsl_dspi {
 	const void				*tx;
 	void					*rx;
 	void					*rx_end;
-	u16					void_write_data;
 	u16					tx_cmd;
 	u8					bits_per_word;
 	u8					bytes_per_word;
@@ -795,8 +793,6 @@ static int dspi_transfer_one_message(struct spi_controller *ctlr,
 				dspi->tx_cmd |= SPI_PUSHR_CMD_CONT;
 		}
 
-		dspi->void_write_data = dspi->cur_chip->void_write_data;
-
 		dspi->tx = transfer->tx_buf;
 		dspi->rx = transfer->rx_buf;
 		dspi->rx_end = dspi->rx + transfer->len;
@@ -897,8 +893,6 @@ static int dspi_setup(struct spi_device *spi)
 		sck_cs_delay = pdata->sck_cs_delay;
 	}
 
-	chip->void_write_data = 0;
-
 	clkrate = clk_get_rate(dspi->clk);
 	hz_to_spi_baud(&pbr, &br, spi->max_speed_hz, clkrate);