drm/amdgpu: fix typo in amdgpu_vce_validate_bo

Otherwise buffer placement is very restrictive and might fail.

Fixes: "drm/amdgpu: fix VCE buffer placement restrictions v2"

Signed-off-by: Christian König <christian.koenig@amd.com>
Reported-by: Deng, Emily <Emily.Deng@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>
Cc: stable@vger.kernel.org