staging:iio:ad7606: Re-add missing scale attribute

staging:iio:ad7606: Re-add missing scale attribute

commit 279bf2e57c30c9a4482b2b6ede11b31c41e35e78 upstream.

Commit 50ac23be ("staging:iio:adc:ad7606 add local define for chan_spec
structures.") accidentally removed the scale info_mask flag. This patch
adds it back again.

Signed-off-by: Lars-Peter Clausen <lars@metafoo.de>
Acked-by: Jonathan Cameron <jic23@kernel.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
[bwh: Backported to 3.2:
 - info_mask was completely gone rather than set to another flag
 - IIO_CHAN_INFO_SCALE_SHARED_BIT was not defined; write it out as a shift]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>