analyze: clarify return value

In this case, EXIT_SUCCESS is the same as 0, but we shouldn't use it
in a function that returns negative on error.

src/analyze/analyze.c

@@ -2099,7 +2099,7 @@ static int dump_timespan(int argc, char *argv[], void *userdata) {
                         putchar('\n');
         }
 
-        return EXIT_SUCCESS;
+        return 0;
 }
 
 static int test_timestamp_one(const char *p) {