parisc: Export iosapic_serial_irq() symbol for serial port driver

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>

drivers/parisc/iosapic.c

@@ -866,6 +866,7 @@ int iosapic_serial_irq(struct parisc_device *dev)
 
 	return vi->txn_irq;
 }
+EXPORT_SYMBOL(iosapic_serial_irq);
 #endif