spi: fsl-espi: fix ioread16/iowrite16 endianness

fsl_espi_read_reg16 / fsl_espi_write_reg16 are supposed to read / write
big endian values. Therefore ioread16be / iowrite16be have to be used.

Fixes: 	05823432

 ("eliminate need for linearization when writing to hardware")
Signed-off-by: Heiner Kallweit <hkallweit1@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>