mAudioHwDevs and related cleanup

Inline AudioFlinger::initCheck and remove unnecessary lock.

Remove redundant check of mAudioHwDevs.size().

No need to lock mHardwareLock for each device separately
during initialization.

Use size_t not int to loop through Vector, since size() returns size_t.

Add missing hardware lock for get_mic_mute() and get_input_buffer_size().

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Change-Id: Iafae78ef78bbf65f703d99fcc27c2f4ff221aedc