vol: initialize readmeinode

vol: initialize readmeinode

Newer gcc complains about readmeinode being potentially used
uninitialized.  Doesn't look possible in the code, but initialize
it to quiet the warning.

Change-Id: I7172475a64a3bfb90a76c0266d7812d5d42a2c4c
Reviewed-on: http://gerrit.openafs.org/6512
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>