spi/pxa2xx: check status register as well to determine if the device is off

The current interrupt handler calls pm_runtime_suspended() to check if the
device is suspended or not. However, runtime PM status of the device is
only set to suspended once all PM runtime suspend hooks have executed.

In case of Intel Lynxpoint we have the device bound to the ACPI power
domain and its runtime suspend hook will put the device to D3hot (or D3cold
if possible). This means that the device is powered off before its state is
set to runtime suspended. While in this state the device might get an
interrupt that is meant for another device (as the interrupt line is
shared), and because the device is powered off accessing its registers will
return 0xffffffff that the driver misinterprets as an invalid state.

When this happens user will see messages like below on the console:

  pxa2xx-spi INT33C0:00: bad message state in interrupt handler

Fix this by checking the status register for ~0 and returning IRQ_NONE in
that case.

Signed-off-by: Mika Westerberg <mika.westerberg@linux.intel.com>
Signed-off-by: Mark Brown <broonie@linaro.org>