um: Do not unlock mutex that is not hold.

Return error instead of trying to unlock a mutex that is not hold.

Signed-off-by: Daniel Walter <dwalter@google.com>
Reviewed-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Acked-by: Anton Ivanov <anton.ivanov@cambridgegreys.com>
Signed-off-by: Richard Weinberger <richard@nod.at>
1 file changed