staging: iio: ak8975: Make it behave better as modules

The memory regions of the probe and remove are move
to __devinit and __devexit respectively.

Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Shubhrajyoti D <shubhrajyoti@ti.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>