simtrace2-sniff.c: fix printf usage

Fixes:

simtrace2-sniff.c:113:4: error: format not a string literal and no format arguments [-Werror=format-security]
    printf(flag_meanings[i].str);

Change-Id: I9793c680f070e724ce89272e9e489963c7516d52
diff --git a/host/src/simtrace2-sniff.c b/host/src/simtrace2-sniff.c
index 7e8e5eb..b2ce4a0 100644
--- a/host/src/simtrace2-sniff.c
+++ b/host/src/simtrace2-sniff.c
@@ -110,7 +110,7 @@
 	uint32_t i;
 	for (i = 0; i < nb_flags; i++) {
 		if (flags & flag_meanings[i].value) {
-			printf(flag_meanings[i].str);
+			printf("%s", flag_meanings[i].str);
 			flags &= ~flag_meanings[i].value;
 			if (flags) {
 				printf(", ");