drivers/tty/serial/sh-sci.h: remove dead reference on ARCH_SH7372

The Kconfig option ARCH_SH7372 has been removed by commit 59b89af1
("ARM: shmobile: sh7372: Remove Legacy C SoC code").  This patch removes
the last reference on this Kconfig option.

Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Acked-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>