Staging: iio: adt7316: Switch irq_flags to a local variable

There is no need to store irq_flags into the structure as it
is always set to the same thing. Hence switch irq_flags to a
local variable.

Signed-off-by: Shreeya Patel <shreeya.patel23498@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>