ptxed: only compute stats when requested

Statistics are currently computed whether or not --stat is specified.  The
option only affects printing statistics at the end.

Do not compute stats if we don't want to print them.

Change-Id: I77e8d6ab4be60b62e706714e6429d1759b83eb44
Signed-off-by: Markus Metzger <markus.t.metzger@intel.com>
diff --git a/ptxed/src/ptxed.c b/ptxed/src/ptxed.c
index a7f2607..3fe5aac 100644
--- a/ptxed/src/ptxed.c
+++ b/ptxed/src/ptxed.c
@@ -1342,7 +1342,8 @@
 
 	xed_tables_init();
 
-	decode(&decoder, iscache, &options, &stats);
+	decode(&decoder, iscache, &options,
+	       options.print_stats ? &stats : NULL);
 
 	if (options.print_stats)
 		print_stats(&stats);