parisc: Export iosapic_serial_irq() symbol for serial port driver

commit a0c9f1f2e53b8eb2ae43987a30e547ba56b4fa18 upstream.

The parisc serial port driver needs this symbol when it's compiled
as module.

Signed-off-by: Helge Deller <deller@gmx.de>
Reported-by: kernel test robot <lkp@intel.com>
Cc: <stable@vger.kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>