Make (extern) declarations and definition of macro_depth consistent

alsa-project/alsa-tools pull request #19 was opened from tautschnig:

All `extern` declarations refer to it as `unsigned int`, but the actual definition is a signed integer.

Reported by CBMC's goto-cc compiler, which performs type-aware linking.

Request URL : https://github.com/alsa-project/alsa-tools/pull/19 Patch URL : https://github.com/alsa-project/alsa-tools/pull/19.patch Repository URL: https://github.com/alsa-project/alsa-tools