iio: Fix IIO_EVENT_CODE_EXTRACT_DIR bit mask

commit ccf54555da9a5e91e454b909ca6a5303c7d6b910 upstream.

The direction field is set on 7 bits, thus we need to AND it with 0111 111 mask
in order to retrieve it, that is 0x7F, not 0xCF as it is now.

Fixes: ade7ef7ba (staging:iio: Differential channel handling)
Signed-off-by: Cristina Ciocan <cristina.ciocan@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>
[bwh: Backported to 3.2: adjust filename]
Signed-off-by: Ben Hutchings <ben@decadent.org.uk>