audio: Fix parsing of arguments in the APM config update script

The regex for finding "-h[elp]" argument wasn't correct.
As a result, a file name containing "-h" would match.
Fix the regex by requiring that "-h" must appear at the
beginning of the line.

Test: h/i/audio/7.0/config/update_audio_policy_config.sh -h
Test: h/i/audio/7.0/config/update_audio_policy_config.sh -help
Test: h/i/audio/7.0/config/update_audio_policy_config.sh test-help.xml
Change-Id: Ibdf191e95baacc8600daa8b2f19ddc8338f182eb