amd64_edac: Get rid of boot_cpu_data accesses

Now that we cache (family, model, stepping) locally, use them instead of
boot_cpu_data.

No functionality change.
Signed-off-by: Borislav Petkov <bp@suse.de>

drivers/edac/amd64_edac.h

@@ -348,7 +348,9 @@ struct amd64_pvt {
 
 	u16 mc_node_id;		/* MC index of this MC node */
 	u8 fam;			/* CPU family */
-	u8 model;		/* CPU model */
+	u8 model;		/* ... model */
+	u8 stepping;		/* ... stepping */
+
 	int ext_model;		/* extended model value of this node */
 	int channel_count;