alsa_conformance_test: Fix incorrect help message and change format

Fix there is not duration in the example of device file.
And change it to the better format.

Old:
alsa_conformance_test -h
        ...
        --device_file: Device file path. It will load devices from the file.
        ...

Device file format:
        [name] [type] [channels] [format] [rate] [period] [block_size] ...
        eg: hw:0,0 PLAYBACK 2 S16_LE 48000 240 240 10 # It's an example

New:
alsa_conformance_test -h
    ...
    --device_file:
        Device file path. It will load devices from the file. File format:
        [name] [type] [channels] [format] [rate] [period] [block_size] ...
        eg: hw:0,0 PLAYBACK 2 S16_LE 48000 240 240 10 # Example

BUG=chromium:941877
TEST=alsa_conformance_test -h

Change-Id: If1ae591aa56e84d7474729e0bb4a2b34059b6dba
Reviewed-on: https://chromium-review.googlesource.com/1521852
Commit-Ready: ChromeOS CL Exonerator Bot <chromiumos-cl-exonerator@appspot.gserviceaccount.com>
Tested-by: Yu-Hsuan Hsu <yuhsuan@chromium.org>
Reviewed-by: Cheng-Yi Chiang <cychiang@chromium.org>
1 file changed