iio: light: vcnl4000: Switch to sparse friendly iio_device_claim/release_direct()

iio: light: vcnl4000: Switch to sparse friendly iio_device_claim/release_direct()

These new functions allow sparse to find failures to release
direct mode reducing chances of bugs over the claim_direct_mode()
functions that are deprecated.

To simplify the code whilst making the change (and avoid potential false
positives from sparse), split the enabling and disabling of thresholds
into separate functions.  This could have been done in two steps
by splitting the functions first, but would have meant rewriting
the enable function twice.

Cc: Astrid Rost <astrid.rost@axis.com>
Tested-by: Per-Daniel Olsson <perdaniel.olsson@axis.com>
Reviewed-by: Per-Daniel Olsson <perdaniel.olsson@axis.com>
Reviewed-by: David Lechner <dlechner@baylibre.com>
Link: https://patch.msgid.link/20250309170633.1347476-18-jic23@kernel.org
Signed-off-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>