Correct pointer type of 'next' field within struct volinfo

Correct pointer type of 'next' field within struct volinfo

Reported by Marcus Watts

The next field of struct volinfo is supposed to be a pointer
to a struct volinfo.

LICENSE IPL10

Reviewed-on: http://gerrit.openafs.org/87
Verified-by: Russ Allbery <rra@stanford.edu>
Reviewed-by: Russ Allbery <rra@stanford.edu>
(cherry picked from commit 47e31b020c3393fdbda9dddd99269482693cfb6c)
Change-Id: I719f6417abc68d5ab2595241b247eeb83cf7affc
Reviewed-on: http://gerrit.openafs.org/930
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>