Convert snd-page-alloc proc file to use seq_file (CVE-2007-4571)

Commit ccec6e2c in mainline.

Use seq_file for the proc file read/write of snd-page-alloc module.
This automatically fixes bugs in the old proc code.

Adrian Bunk:
Backported to 2.6.16.

Signed-off-by: Takashi Iwai <tiwai@suse.de>
Signed-off-by: Adrian Bunk <bunk@kernel.org>