serial: of_serial: do not set port.type twice

The port.type has already been set by of_platform_serial_setup()
called from a few lines above.
Setting it to the same value is redundant.

Signed-off-by: Masahiro Yamada <yamada.masahiro@socionext.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>