fix:修复statfs函数内部判断错误

修复函数调用的是statfs却用stat!=NULL来判断，当文件系统是little_fs时导致死机的问题。

close #I69BXB

Signed-off-by: yinjiaming <yinjiaming@huawei.com>
Change-Id: Ib9784c017f4260433c3f12e352470108ea83ec19

components/fs/vfs/vfs_fs.c

@@ -750,7 +750,7 @@ int statfs(const char *path, struct statfs *buf)
         return MapToPosixRet(ret);
     }
 
-    if (mp->mFs->fsFops->stat != NULL) {
+    if (mp->mFs->fsMops->statfs != NULL) {
         ret = mp->mFs->fsMops->statfs(pathInMp, buf);
     } else {
         VFS_ERRNO_SET(ENOTSUP);