drm/amdgpu/mes12: add missing opcode string

Fixes the indexing of the string array.
Reviewed-by: Hawking Zhang <Hawking.Zhang@amd.com>
Signed-off-by: Alex Deucher <alexander.deucher@amd.com>

drivers/gpu/drm/amd/amdgpu/mes_v12_0.c

@@ -99,6 +99,7 @@ static const char *mes_v12_0_opcodes[] = {
 	"SET_LOG_BUFFER",
 	"CHANGE_GANG_PRORITY",
 	"QUERY_SCHEDULER_STATUS",
+	"unused",
 	"SET_DEBUG_VMID",
 	"MISC",
 	"UPDATE_ROOT_PAGE_TABLE",