volser: Don't declare cstruct twice

volser: Don't declare cstruct twice

Both vsprocs.c and vsutils.c declare the global variable 'cstruct'
(which is initialised by vos.c in order to pass a ubik client structure
through to many of the libvolser functions). This double declaration
prevents libvolser from being linked as a shared library on some
platforms. We only need one of these, so just make vsprocs.c declare it,
and vsutils.c refer to it as an extern.

Of course, using a global variable to pass state around is really quite
nasty, but let's fix that in another change.

Change-Id: Ief1667bd7a5b70dbfb49cdc02cc435eb2344527e
Reviewed-on: http://gerrit.openafs.org/5362
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>
Reviewed-by: Jeffrey Altman <jaltman@openafs.org>
Tested-by: Jeffrey Altman <jaltman@openafs.org>