iio: humidity: am2315: Remove a stray unlock

We haven't taken the lock yet so we don't need to unlock here.

Fixes: 0d96d5ea ('iio: humidity: Add triggered buffer support for AM2315')
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Acked-by: Tiberiu Breana <tiberiu.a.breana@intel.com>
Signed-off-by: Jonathan Cameron <jic23@kernel.org>