Fix typo in cm_dcache.c

Fix typo in cm_dcache.c

Commit b85c5f9339e20d3de9b1316217dadbea41ad537e introduced a new
memset() but left out a prenthesis.

In the absence of a windows build machine, this error went unnoticed.

Reported by Mark Vitale.

Change-Id: Ie250163029132896cd70dc822c6170913e83dafe
Reviewed-on: https://gerrit.openafs.org/12241
Reviewed-by: Michael Meffie <mmeffie@sinenomine.net>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Tested-by: Michael Meffie <mmeffie@sinenomine.net>
Reviewed-by: Stephan Wiesand <stephan.wiesand@desy.de>
Reviewed-by: Benjamin Kaduk <kaduk@mit.edu>