drm/amd/amdgpu: vcn10 Add callback for emit_reg_write_reg_wait

The callback .emit_reg_write_reg_wait was missing for vcn decode
which resulted in a kernel oops.

Signed-off-by: Tom St Denis <tom.stdenis@amd.com>
Reviewed-by: Andrey Grodzovsky <andrey.grodzovsky@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>