serial: Delete dead code for CIR serial ports

Commit e4fda3a0 ("serial: don't register CIR serial ports") adds a
check for PORT_8250_CIR to serial8250_register_8250_port(). But the code
isn't needed as the function never takes the branch when the port is CIR
serial port.

This patch deletes the dead code.

Signed-off-by: Matthias Brugger <mbrugger@suse.com>
Reviewed-by: Andy Shevchenko <andy.shevchenko@gmail.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>