libc/stdio: lib_fwrite_unlocked must call lib_fflush_unlocked with true

otherwise the following file i/o mess up the output

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

libs/libc/stdio/lib_libfwrite.c

@@ -130,7 +130,7 @@ ssize_t lib_fwrite_unlocked(FAR const void *ptr, size_t count,
         {
           /* Flush the buffered data to the IO stream */
 
-          int bytes_buffered = lib_fflush_unlocked(stream, false);
+          int bytes_buffered = lib_fflush_unlocked(stream, true);
           if (bytes_buffered < 0)
             {
               goto errout;