[Why]
We're still missing a few and we'd like to avoid continuining when
a hang occurs for debug purposes.

[How]
Add the loop anywhere we try to wait on rptr == wptr in dc_dmub_srv.
Reviewed-by: Ovidiu Bunea <ovidiu.bunea@amd.com>
Acked-by: Hamza Mahfooz <hamza.mahfooz@amd.com>
Signed-off-by: Nicholas Kazlauskas <nicholas.kazlauskas@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>