serial: sh-sci: Simplify multiplication/shift logic

"a * (1 << b)" == "a << b".

No change in generated code.

Reviewed-by: Ulrich Hecht <uli+renesas@fpond.eu>
Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Link: https://lore.kernel.org/r/118d62e167f6cf5e98bdf9a738634b4590ea8d09.1645460901.git.geert+renesas@glider.be


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>