[x264-devel] [patch]fix a mutex init error

[BugMaster]

On Thu, 30 Mar 2017 10:54:37 +0800, Shi Qiu wrote:
> It seems that cost_ref_mutex is used now, but now inited. (May crash some times)

UNUSED attribute was probably accidently added in
http://git.videolan.org/?p=x264/x264-sandbox.git;a=commit;h=30b3825ed00f7f88397a26760cac5248f2f8e226 
As for x264_pthread_mutex_init/x264_pthread_mutex_destroy they are not
needed here because it use global mutex of X264_PTHREAD_MUTEX_INITIALIZER