venus: Make clang happy with strlcpy use

venus: Make clang happy with strlcpy use

clang now expects that strlcpy will always be used to prevent overflow
of the destination string, and gives a warning if the size parameter is
based solely on the length of the source string.

Modify the BreakUpPath function so that it takes the size of the
destination string as an argument, and uses this to limit the amount of
data pasted into it.

Change-Id: I86f68dd2013ca8bc4c88ade78d27c4d416a9ae94
Reviewed-on: http://gerrit.openafs.org/7086
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Derrick Brashear <shadow@dementix.org>