The "download" link asks you to download a file (for me) called "download.php". This is a bzip2 archive containing a diff file.
If you want it to have a reasonable name, do:"mv download.php alsa_patch_au8820.diff.bz2".
To read the patch you could do: "bzcat alsa_patch_au8820.diff.bz2 | less". Notice the first three lines:
diff -Naur alsa-driver-0.9.2_orig/acinclude.m4 alsa-driver-0.9.2_vortex/acinclude.m4
--- alsa-driver-0.9.2_orig/acinclude.m4 2003-03-19 14:50:20.000000000 -0400
+++ alsa-driver-0.9.2_vortex/acinclude.m4 2003-03-26 01:26:14.000000000 -0400
Here he diffs the old file "alsa-driver-0.9.2_orig/acinclude.m4" with the new file "alsa-driver-0.9.2_vortex/acinclude.m4". Since the dir is alsa-driver-0.9.2_vortex, I believe you need a source package (tarball) called something like alsa-driver-0.9.2*.tar.gz.
Unpack that tarball, which should give you a directory called something like alsa-driver-0.9.2, then run "bzcat alsa_patch_au8820.diff.bz2 | patch --dry-run ./alsa-driver-0.9.2" to test (option --dry-run) if that will work. If it does, you can remove "--dry-run", else you'll possibly have to tweak the -p options (man patch).