man: Correct "rate" option

[GitHub pull_request - edited]

alsa-project/alsa-utils pull request #83 was edited from nootc:

Resolves https://github.com/alsa-project/alsa-utils/issues/82
Change "rate" option from "-c" to "-r".

Request URL   : https://github.com/alsa-project/alsa-utils/pull/83
Patch URL     : https://github.com/alsa-project/alsa-utils/pull/83.patch
Repository URL: https://github.com/alsa-project/alsa-utils