arcam_av.c: Include missing string.h

[GitHub pull_request - opened <github@xxxxxxxxxxxxxxxx>]

alsa-project/alsa-plugins pull request #47 was opened from kraj:

bzero() function needs this header to be included

Signed-off-by: Khem Raj <raj.khem@xxxxxxxxx>

Request URL   : https://github.com/alsa-project/alsa-plugins/pull/47
Patch URL     : https://github.com/alsa-project/alsa-plugins/pull/47.patch
Repository URL: https://github.com/alsa-project/alsa-plugins