staging: zcache: fix uninitialized variable compile warning

[V2: no code changes, patchset now generated via git format-patch -M]

Fix unitialized variable in zcache which generates warning during build

Signed-off-by: Dan Magenheimer <dan.magenheimer@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>