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 <[e-mail]>
Reported-by: kernel test robot <[e-mail]>
Cc: <[e-mail]>

drivers/parisc/iosapic.c

···
 
 	return vi->txn_irq;
 }
+EXPORT_SYMBOL(iosapic_serial_irq);
 #endif