spi: spi-ep93xx: Fix API slippage

ep93xx_spi_read_write() changed is parameters, but the function
documentation was left unchanged.  Let's realign.

Fixes the following W=1 kernel build warning(s):

 drivers/spi/spi-ep93xx.c:227: warning: Function parameter or member 'master' not described in 'ep93xx_spi_read_write'
 drivers/spi/spi-ep93xx.c:227: warning: Excess function parameter 'espi' description in 'ep93xx_spi_read_write'
Signed-off-by: Lee Jones <lee.jones@linaro.org>
Cc: Mika Westerberg <mika.westerberg@iki.fi>
Link: https://lore.kernel.org/r/20200717135424.2442271-5-lee.jones@linaro.orgSigned-off-by: Mark Brown <broonie@kernel.org>

drivers/spi/spi-ep93xx.c

@@ -214,7 +214,7 @@ static void ep93xx_do_read(struct spi_master *master)
 
 /**
  * ep93xx_spi_read_write() - perform next RX/TX transfer
- * @espi: ep93xx SPI controller struct
+ * @master: SPI master
  *
  * This function transfers next bytes (or half-words) to/from RX/TX FIFOs. If
  * called several times, the whole transfer will be completed. Returns