Doc: Fix spelling

Legned -> Legend
mainatined -> maintained

Legend is now Lenovo, so more fixes (text and url)
would be possible, too.

Cc: Jiri Kosina <trivial@kernel.org>
Cc: linux-doc@vger.kernel.org
Cc: linux-kernel@vger.kernel.org
Signed-off-by: Stefan Weil <weil@mail.berlios.de>
Signed-off-by: Jiri Kosina <jkosina@suse.cz>