Replace uintptr_t type cast with uintptrsz in afs_vcache.c

Replace uintptr_t type cast with uintptrsz in afs_vcache.c

A recent change (commit 80fe111f0044aa7a67215ad92210dc72cb7eb2c0)
to afs_vcache.c contains a call to afs_warn() whose second parameter
contains a "(uintptr_t)" type cast as part of a double type cast.
This presents an issue on some systems, such as OpenBSD, where this
object type is defined in a header that is not presently included.
This change modifies that type cast to instead use the AFS-internal
"(uintptrsz)" type which should provide the same effect.

Note that an earlier version of this patch attempted to remove the
"offending" type cast as redundant but it was pointed out that some
systems require this kind of cascading type cast when casting pointers
to integers to deal with possible size issues.

Reviewed-on: http://gerrit.openafs.org/4671
Reviewed-by: Derrick Brashear <shadow@dementia.org>
Tested-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit b3004fbd5007d400a4cd3fb2a5b1c52d98618aab)

Change-Id: I3c7452d1f09dc7fdbcffe9b047e4ec682ac6ea03
Reviewed-on: http://gerrit.openafs.org/4705
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>