Make sure that mutex is released upon register writing failure.
This fixes boot freezing observed on ARM based OLPC
(http://dev.laptop.org/ticket/11357).
Signed-off-by: NPaul Fox <pgf@laptop.org>
Signed-off-by: NTai-hwa Liang <avatar@sentelic.com>
Signed-off-by: NDmitry Torokhov <dtor@mail.ru>