spi: Use void pointers for data in simple SPI I/O operations

Currently the simple SPI I/O operations all take pointers to u8 * buffers
to operate on. This creates needless type compatibility issues and the
underlying spi_transfer structure uses void pointers anyway so convert the
API over to take void pointers too.

Signed-off-by: Mark Brown <broonie@opensource.wolfsonmicro.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>

drivers/spi/spi.c

@@ -1047,8 +1047,8 @@ static u8	*buf;
  * spi_{async,sync}() calls with dma-safe buffers.
  */
 int spi_write_then_read(struct spi_device *spi,
-		const u8 *txbuf, unsigned n_tx,
-		u8 *rxbuf, unsigned n_rx)
+		const void *txbuf, unsigned n_tx,
+		void *rxbuf, unsigned n_rx)
 {
 	static DEFINE_MUTEX(lock);