serial: export fsl8250_handle_irq

fsl8250_handle_irq is now used by the of_serial driver, and that fails
if it is a loadable module:

ERROR: "fsl8250_handle_irq" [drivers/tty/serial/of_serial.ko] undefined!

This exports the symbol to avoid randconfig errors.
Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Fixes: d43b54d2 ("serial: Enable Freescale 16550 workaround on arm")
Cc: Scott Wood <scottwood@freescale.com>
Signed-off-by: Jeff Mahoney <jeffm@suse.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/tty/serial/8250/8250_fsl.c

@@ -60,3 +60,4 @@ int fsl8250_handle_irq(struct uart_port *port)
 	spin_unlock_irqrestore(&up->port.lock, flags);
 	return 1;
 }
+EXPORT_SYMBOL_GPL(fsl8250_handle_irq);