serial/sunzilog: fix keyboard on SUN SPARCstation

The keyboard on my SUN SPARCstation 5 no longer worked.

    The culprint was: d4e33fac2408d37f7b52e80ca2a89f9fb482914f
    ("serial: Kill off NO_IRQ")

Fix up logic for no irq / irq so the keyboard works again.

Signed-off-by: Sam Ravnborg <sam@ravnborg.org>
Cc: Alan Cox <alan@linux.intel.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>