iio: magnetometer: Remove IRQF_ONESHOT

Passing IRQF_ONESHOT ensures that the interrupt source is masked until
the secondary (threaded) handler is done. If only a primary handler is
used then the flag makes no sense because the interrupt can not fire
(again) while its handler is running.
The flag also disallows force-threading of the primary handler and the
irq-core will warn about this.
The force-threading functionality is required on PREEMPT_RT because the
handler is using locks with can sleep on PREEMPT_RT.

Remove IRQF_ONESHOT from irqflags.

Tested-by: Geert Uytterhoeven <geert+renesas@glider.be>
Signed-off-by: Sebastian Andrzej Siewior <bigeasy@linutronix.de>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@intel.com>
Reviewed-by: Nuno Sá <nuno.sa@analog.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>