iio: mma8452: Fix ignoring MMA8452_INT_DRDY

Interrupts are ignored if no event bit is set in the status status
register and this breaks the buffer interface. No data is shown when
running "iio_generic_buffer -n mma8451 -a" and interrupt counts go
crazy.

Fix by not returning IRQ_NONE if DRDY is set.

Fixes: 605f72de

 ("iio: accel: mma8452: improvements to handle
multiple events")

Signed-off-by: Leonard Crestez <leonard.crestez@nxp.com>
cc: <Stable@vger.kernel.org>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>