drm/amdgpu:Fixed wrong emit frame size for enc

Emit frame size should match with corresponding function,
uvd_v6_0_enc_ring_emit_vm_flush has 5 amdgpu_ring_write

Signed-off-by: James Zhu <James.Zhu@amd.com>
Reviewed-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>