drm/amd/display: Reset OUTBOX0 r/w pointer on DMUB reset

[Why & How]
We missed resetting OUTBOX0 mailbox r/w pointer on DMUB reset.
Fix it.

Fixes: 6ecf9773 ("drm/amd/display: Fix DMUB outbox trace in S4 (#4465)")
Signed-off-by: Cruise Hung <Cruise.Hung@amd.com>
Acked-by: Aurabindo Pillai <aurabindo.pillai@amd.com>
Tested-by: Daniel Wheeler <daniel.wheeler@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/display/dmub/src/dmub_dcn32.c

@@ -130,6 +130,8 @@ void dmub_dcn32_reset(struct dmub_srv *dmub)
 	REG_WRITE(DMCUB_INBOX1_WPTR, 0);
 	REG_WRITE(DMCUB_OUTBOX1_RPTR, 0);
 	REG_WRITE(DMCUB_OUTBOX1_WPTR, 0);
+	REG_WRITE(DMCUB_OUTBOX0_RPTR, 0);
+	REG_WRITE(DMCUB_OUTBOX0_WPTR, 0);
 	REG_WRITE(DMCUB_SCRATCH0, 0);
 }