spi: sh-msiof: Fix FIFO size to 64 word from 256 word

commit fe78d0b7 upstream.

The upper limit of Tx/Rx FIFO size is 64 word by the
specification of H/W. This patch corrects to 64 word from 256 word.

Signed-off-by: Koji Matsuoka <koji.matsuoka.xm@renesas.com>
Signed-off-by: Yoshihiro Kaneko <ykaneko0929@gmail.com>
Signed-off-by: Mark Brown <broonie@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>