Linux: fix permission op test for certain compilers

Linux: fix permission op test for certain compilers

Some compilers complain that _inode is used uninitialised here.
Since this test requires -Werror, it causes the test to fail
and our permission op to be used in RCU mode, leading to lockups.

Initialise it to make the compilers happy.

Fixes a lockup seen on kernels 2.6.38+ on Gentoo and Debian.

Reviewed-on: http://gerrit.openafs.org/4654
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>
(cherry picked from commit 050945e949135c1b98ed353fc05fcf9b8c1587bd)

Change-Id: Icc4e65946c8d04bd519c95b969dec1d2359dce51
Reviewed-on: http://gerrit.openafs.org/4655
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementia.org>