serial: liteuart: don't set unused port fields

Remove regshift and iobase port fields, since they are unused
by the driver.

Signed-off-by: Gabriel Somlo <gsomlo@gmail.com>
Reviewed-by: Geert Uytterhoeven <geert@linux-m68k.org>
Reviewed-by: Jiri Slaby <jirislaby@kernel.org>
Link: https://lore.kernel.org/r/20221123130500.1030189-5-gsomlo@gmail.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>