staging:iio:accel:adis16209: Fix double registration of in_incli0_index

iio (null): tried to double register : in_incli0_index

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