vol: Don't use MAX_INT when UINT_MAX will do

vol: Don't use MAX_INT when UINT_MAX will do

limits.h provides us with UINT_MAX, so use this for the maxmimum
size of an unsigned integer, rather than trying to grow our own.

Change-Id: Ia23c45a9e295589929374a8324ea2b3d268ae6c0
Reviewed-on: http://gerrit.openafs.org/4420
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>