h8300: drivers/serial/Kconfig was moved

commit ab4382d2 moved
drivers/serial/Kconfig to drivers/tty/serial/Kconfig, so we need to
source the latter file.

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>