libafscp: Don't free bogus ptr in ResolvPathFromVol

libafscp: Don't free bogus ptr in ResolvPathFromVol

afscp_ResolvPathFromVol makes a copy of the path passed to it using
strdup. It then iterates across that, removing initial '/' characters.
However, this iteration means that 'p' no longer points to the start
of the allocated memory - when we free 'p', we may actually be freeing
an offset into the block, which will make malloc unhappy.

Make a copy of the result from strdup, and use that to free the block.

Caught by clang-analyzer

Change-Id: I0e7d8c7cf3b70baa4868c65fb4c3a32474557628
Reviewed-on: http://gerrit.openafs.org/9196
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>