efifb: Don't show the mapping VA

The framebuffer mapping virtual address leaks information about the
kernel memory layout.  Stop logging it.

Cc: Peter Jones <pjones@redhat.com>
Cc: Jean-Christophe Plagniol-Villard <plagnioj@jcrosoft.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: linux-fbdev@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Andy Lutomirski <luto@kernel.org>
Signed-off-by: Peter Jones <pjones@redhat.com>
Signed-off-by: Tomi Valkeinen <tomi.valkeinen@ti.com>