lib/vasprintf: Shouldn't call va_end(ap) to avoid the double free

Signed-off-by: Xiang Xiao <xiaoxiang@xiaomi.com>

libs/libc/stdio/lib_vasprintf.c

@@ -93,7 +93,6 @@ int vasprintf(FAR char **ptr, FAR const IPTR char *fmt, va_list ap)
   buf = (FAR char *)lib_malloc(nulloutstream.nput + 1);
   if (!buf)
     {
-      va_end(ap);
 #ifdef va_copy
       va_end(ap2);
 #endif
@@ -119,8 +118,6 @@ int vasprintf(FAR char **ptr, FAR const IPTR char *fmt, va_list ap)
                         fmt, ap);
 #endif
 
-  va_end(ap);
-
   /* Return a pointer to the string to the caller.  NOTE: the memstream put()
    * method has already added the NUL terminator to the end of the string
    * (not included in the nput count).