staging:iio:various move default scan mask setting after ring register or remove

The scan mask will be dynamically assigned in register, so don't
use it before that.

In adis16260 I've moved it as I know this driver has userspace code.
Same for sca3000 where it is cost free due to hardware buffer.
Can do that for the others, but in theory userspace code should always
have been checking these and setting them appropriately anyway!

V2: Clear default mask out of adis16400 as reported by Michael

Signed-off-by: Jonathan Cameron <jic23@cam.ac.uk>
Reported-by: Michael Hennerich <michael.hennerich@analog.com>
Acked-by: Michael Hennerich <Michael.Hennerich@analog.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>