spi: fix spi_write_then_read() comment

Buffer needs not be dma-safe, not rx data length.
Signed-off-by: NJiri Pirko <jpirko@redhat.com>
Cc: David Brownell <david-b@pacbell.net>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>

drivers/spi/spi.c

@@ -700,8 +700,8 @@ static u8	*buf;
  * @spi: device with which data will be exchanged
  * @txbuf: data to be written (need not be dma-safe)
  * @n_tx: size of txbuf, in bytes
- * @rxbuf: buffer into which data will be read
- * @n_rx: size of rxbuf, in bytes (need not be dma-safe)
+ * @rxbuf: buffer into which data will be read (need not be dma-safe)
+ * @n_rx: size of rxbuf, in bytes
  * Context: can sleep
  *
  * This performs a half duplex MicroWire style transaction with the