drm/amdgpu/vm: Check PRT uAPI flag instead of PTE flag

drm/amdgpu/vm: Check PRT uAPI flag instead of PTE flag

This fixes sparse mappings (aka. partially resident textures).

Check the correct flags.
Since a recent refactor, the code works with uAPI flags (for
mapping buffer objects), and not PTE (page table entry) flags.

Fixes: 6716a823d18d ("drm/amdgpu: rework how PTE flags are generated v3")
Signed-off-by: Timur Kristóf <timur.kristof@gmail.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>