fs: Free parent_dir later in lsmount and flushmount

If lsmount or flushmount encounter an error, then they may include
the contents of parent_dir in their error message. However, in both
cases, this was freed a couple of lines earlier.

Just move the free() later, so that the contents of this variable
are still available.

Caught by clang-analyzer

Change-Id: Ideba52b7ba98f034baf923194007239a6cf0221f
Reviewed-on: http://gerrit.openafs.org/9193
Reviewed-by: Derrick Brashear <shadow@your-file-system.com>
Tested-by: BuildBot <buildbot@rampaginggeek.com>
Reviewed-by: Jeffrey Altman <jaltman@your-file-system.com>