pcm: Return unsigned int if error occurs by `read` or `write` system call

[GitHub pull_request - opened]

alsa-project/alsa-lib pull request #242 was opened from Korilakkuma:

`read` or `write` system call returns `-1` if error occurs.

Request URL   : https://github.com/alsa-project/alsa-lib/pull/242
Patch URL     : https://github.com/alsa-project/alsa-lib/pull/242.patch
Repository URL: https://github.com/alsa-project/alsa-lib