staging: iio: adis16209: Remove exceptional & on function name

Remove & from function pointers to conform to the style found elsewhere
in the file.  Done using the following semantic patch

// <smpl>
@r@
identifier f;
@@

f(...) { ... }
@@
identifier r.f;
@@

- &f
+ f
// </smpl>

Signed-off-by: simran singhal <singhalsimran0@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>