iio: accel: adxl345: reorganize irq handler

iio: accel: adxl345: reorganize irq handler

Reorganize the IRQ handler. Move the overrun handling to the bottom.
Overrun leads to reset the interrupt register. This also happens at
evaluation of a particular interrupt event. First evaluate an event
if possible, then fall back to overrun handling. Additionally simplify
fetching the interrupt status function.

Both is in preparation to build interrupt handling up for the handling
of different detected events, implemented in follow up patches.

Signed-off-by: Lothar Rubusch <l.rubusch@gmail.com>
Link: https://patch.msgid.link/20250220104234.40958-4-l.rubusch@gmail.com
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>