libmediaplayerservice: unlock before trying to reclaim drm session.

    status_t err = mPlugin->openSession(sessionId);

    if (err == ERROR_DRM_RESOURCE_BUSY) {

        bool retry = false;

        mLock.unlock();

        // reclaimSession may call back to closeSession, since mLock is shared between Drm

        // instances, we should unlock here to avoid deadlock.

        retry = DrmSessionManager::Instance()->reclaimSession(getCallingPid());

        mLock.lock();

        if (mInitCheck != OK) {

            return mInitCheck;

        }

        if (mPlugin == NULL) {

            return -EINVAL;

        }

        if (retry) {

            err = mPlugin->openSession(sessionId);

        }