iio:temperature:tmp006 put sampling_frequency in info_mask_shared_by_all

Doing this makes it possible to access this control from within the kernel.

Signed-off-by: Jonathan Cameron <jic23@kernel.org>
Acked-by: Peter Meerwald <pmeerw@pmeerw.net>
Reviewed-by: Lars-Peter Clausen <lars@metafoo.de>