Staging: iio: adc: ad7280a.c: Fixed Macro argument reuse

CHECK: Macro argument reuse 'addr' - possible side-effects?

convert AD7280A_DEVADDR to ad7280a_devaddr static function
to fix checkpath check

v3: small style changes

Signed-off-by: Jaya Durga <rjdurga@gmail.com>
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>