gpu: nova-core: Simplify `DmaObject::from_data` in nova-core/dma.rs

gpu: nova-core: Simplify `DmaObject::from_data` in nova-core/dma.rs

This patch solves one of the existing mentions of COHA, a task
in the Nova task list about improving the `CoherentAllocation` API.
It uses the `write` method from `CoherentAllocation`.

Signed-off-by: Daniel del Castillo <delcastillodelarosadaniel@gmail.com>
[acourbot@nvidia.com: set prefix to "gpu: nova-core:".]
Signed-off-by: Alexandre Courbot <acourbot@nvidia.com>
Message-ID: <20251104193756.57726-3-delcastillodelarosadaniel@gmail.com>