TTY: serial/m32r_sio, simplify old_serial_port

The only variables in old_serial_port are port and irq. So make
old_serial_port contain only those two and move the initialization of
the rest to the place where old_serial_port is actually read.

Also get rid of SERIAL_PORT_DFNS. It is ugly and having the
initializer where it belongs makes more sense. Finally, use already
defined UART_NR in the loop.

Signed-off-by: Jiri Slaby <jslaby@suse.cz>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>