serial: sh-sci: Remove redundant instances of EARLYCON_DECLARE()

As of commit 2eaa7909

 ("earlycon: Use common framework for
earlycon declarations") it is no longer needer to specify both
EARLYCON_DECLARE() and OF_EARLYCON_DECLARE().

Signed-off-by: Geert Uytterhoeven <geert+renesas@glider.be>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>