modify the locking buffer->mutex to include surface_commit

modify the locking buffer->mutex to include surface_commit

 - In the case when _thread_wl_surface_commit() is called after
  the mutex of wl_egl_buffer has been unlocked in the thread,
  the wl_egl_buffer may be freed in the parent thread.
 - In that case, a problem occurs during commit operation.
  Therefore, the buffer must be maintained until the commit is completed.

Change-Id: I994b4ed1a1c8670d3f6f25ec580681875ece7c0a
Signed-off-by: Joonbum Ko <joonbum.ko@samsung.com>