util/time: fix TimeDifferenceMicros microseconds computation

Ticket: 8073

Currently only used in pcap logging for flushing

(cherry picked from commit b21c93d789)

src/util-time.c

@@ -643,5 +643,5 @@ uint64_t SCTimespecAsEpochMillis(const struct timespec* ts)
 
 uint64_t TimeDifferenceMicros(struct timeval t0, struct timeval t1)
 {
-    return (uint64_t)(t1.tv_sec - t0.tv_sec) * 1000000L + (t1.tv_usec - t1.tv_usec);
+    return (uint64_t)(t1.tv_sec - t0.tv_sec) * 1000000L + (t1.tv_usec - t0.tv_usec);
 }