[directfb] Add missing error status

We jumped to the ERROR path without setting an error status - assume
NO_MEMORY.

src/cairo-directfb-surface.c

@@ -405,6 +405,7 @@ _directfb_acquire_surface (cairo_directfb_surface_t  *surface,
 
     if (buffer->Lock (buffer, lock_flags, &data, &pitch)) {
         D_DEBUG_AT (CairoDFB_Acquire, "Couldn't lock surface!\n");
+	status = _cairo_error (CAIRO_STATUS_NO_MEMORY);
         goto ERROR;
     }