serial: sh-sci: fix common SCIFB regmap definition

serial: sh-sci: fix common SCIFB regmap definition

About FIFO count, there are two variants of SCIFs which show
a) TX count in upper, RX count in lower byte of FDR register
b) TX count in TFDR register, RX count in RFDR register

Common SCIFB regmap in current source code is defined as "a".
At least 7372 and 73a0 HW manual say their SICFB are "b".

This patch alters the definition to "b", considering the current
one has come from a mistake. The reason is as follows.

The flag SCIFB sh-sci driver means it has 256 byte FIFO.
The count is from 0(empty) to 256(full), that makes 9-bit.
Because FDR is 16-bit register, it can not hold two 9-bits.
That's why, SCIFB can not be "a".

Signed-off-by: Takashi Yoshii <takashi.yoshii.zj@renesas.com>
Signed-off-by: Shinya Kuribayashi <shinya.kuribayashi.px@renesas.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>