iio: chemical: atlas-ph-sensor: fix typo in val assignment

Fix an incorrect assignment due to a typo on a variable name. The
variable val2 should be assigned 100000 and not val.

Signed-off-by: Colin Ian King <colin.king@canonical.com>
Reviewed-By: Matt Ranostay <mranostay@gmail.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>