spi: sh-hspi: modify write/read method

Current sh-hspi had wrong write/read method which was not linux standard.
If spi_transfer requests tx[2], rx[2] len=2,
then, driver should run tx[0], rx[0], tx[1], rx[1].
But current sh-hspi runs tx[0], tx[1], rx[0], rx[1].
This patch fixes it up.

Signed-off-by: Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>