gcov.c: deal compile warming

gcov.c:61:6: warning: 'path' may be used uninitialized [-Wmaybe-uninitialized]
   61 |   if (path == NULL || access(path, F_OK) != 0 || atoi(strip) <= 0)
      |      ^
gcov.c: In function 'gcov_main':
gcov.c:79:19: note: 'path' was declared here
   79 |   FAR const char *path;

Signed-off-by: wangmingrong1 <[email protected]>

system/gcov/gcov.c

@@ -76,7 +76,7 @@ static void gcov_dump(FAR const char * path, FAR const char *strip)
 int main(int argc, FAR char *argv[])
 {
   FAR const char *strip = "99";
-  FAR const char *path;
+  FAR const char *path = NULL;
   int option;
 
   if (argc < 2)