ecore_drm: Update device copy of framebuffer after page flip completes

The device struct is API, so its copy of the fb pointer needs to be
kept in sync with the output struct's.  We do this when the flip completes
to try to prevent access to an fb that's about to flip.

This fixes Enlightenment screenshots.

@fix

src/lib/ecore_drm/ecore_drm_device.c

@@ -83,6 +83,8 @@ _ecore_drm_device_cb_page_flip(int fd EINA_UNUSED, unsigned int frame EINA_UNUSE
         ecore_drm_output_free(output);
         return;
      }
+
+   output->dev->current = output->current;
    /* We were unable to queue a page on the last flip attempt, so we'll
     * try again now. */
    next = output->next;