uio_pdrv_genirq: fix use without device tree and no interrupt

commit bf12fdf0 upstream.

While e3a3c3a2 ("UIO: fix uio_pdrv_genirq with device tree but no
interrupt") added support for using uio_pdrv_genirq for devices without
interrupt for device tree platforms, the removal of uio_pdrv in
26dac3c4 ("uio: Remove uio_pdrv and use uio_pdrv_genirq instead")
broke the support for non device tree platforms.

This change fixes this, so that uio_pdrv_genirq can be used without
interrupt on all platforms.

This still leaves the support that uio_pdrv had for custom interrupt
handler lacking, as uio_pdrv_genirq does not handle it (yet).

Fixes: 26dac3c4

 ("uio: Remove uio_pdrv and use uio_pdrv_genirq instead")
Signed-off-by: Esben Haabendal <esben@geanix.com>
Cc: stable@vger.kernel.org
Link: https://lore.kernel.org/r/20200701145659.3978-3-esben@geanix.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>