programmer: Move .max_rom_decode into struct master_common

This is useful information from a chipdriver perspective. It also saves
us the open-coded tracking of the "registered master" in `cli_classic.c`
right away.

Change-Id: I532e9b1802184520852fe0b45650239ea252a60d
Signed-off-by: Nico Huber <nico.h@gmx.de>
Reviewed-on: https://review.sourcearcade.org/c/flashprog/+/430
diff --git a/opaque.c b/opaque.c
index f03b70a..f54a032 100644
--- a/opaque.c
+++ b/opaque.c
@@ -63,10 +63,12 @@
 			 __func__);
 		return ERROR_FLASHPROG_BUG;
 	}
-	rmst.max_rom_decode = MAX_ROM_DECODE_UNLIMITED;
 	rmst.buses_supported = BUS_PROG;
 	rmst.opaque = *mst;
 	if (data)
 		rmst.opaque.data = data;
+
+	rmst.common.max_rom_decode = MAX_ROM_DECODE_UNLIMITED;
+
 	return register_master(&rmst);
 }