drm/amdgpu: Make amdgpu_vm_flush() non-failing in submission path

drm/amdgpu: Make amdgpu_vm_flush() non-failing in submission path

amdgpu_vm_flush() is used during job submission and is not expected to
fail. Convert it to return void and simplify the caller.

Initialize the COND_EXEC patch location to 0 so it is safe to call
amdgpu_ring_patch_cond_exec() when init_cond_exec is not supported.

Suggested-by: Christian König <christian.koenig@amd.com>
Cc: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Srinivasan Shanmugam <srinivasan.shanmugam@amd.com>
Reviewed-by: Alex Deucher <alexander.deucher@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>