Ensure update queue new ring buffer is mapped on GPU with correct size.

Decrease queue old ring_bo queue_refcount and increase new ring_bo
queue_refcount.
Signed-off-by: Philip Yang <Philip.Yang@amd.com>
Reviewed-by: Felix Kuehling <felix.kuehling@amd.com>
Acked-by: Christian König <christian.koenig@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>