drm/amdgpu: Remove verify_access shortcut for KFD BOs

This shortcut is no longer needed with access managed properly by KFD.

Signed-off-by: Felix Kuehling <Felix.Kuehling@amd.com>
Reviewed-by: Philip Yang <Philip.Yang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>