serial: sh-sci: Fix a comment about SCIFA

serial: sh-sci: Fix a comment about SCIFA

The comment was correct when it was added, at that time RZ/T1 was
the only SoC in the RZ/T line. Since then, further SoCs have been
added with RZ/T names which do not use the same SCIFA register
layout and so the comment is now misleading.

So we update the comment to explicitly reference only RZ/T1 SoCs.

Reviewed-by: Paul Barker <paul.barker.ct@bp.renesas.com>
Reviewed-by: Wolfram Sang <wsa+renesas@sang-engineering.com>
Reviewed-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Thierry Bultel <thierry.bultel.yh@bp.renesas.com>
Link: https://lore.kernel.org/r/20250403212919.1137670-8-thierry.bultel.yh@bp.renesas.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>