xfsdump: Fix memory leak

Fix memory leak found by coverity.

>>>     CID 1554295:  Resource leaks  (RESOURCE_LEAK)
>>>     Failing to save or free storage allocated by strdup(path) leaks it.

Reviewed-by: "Darrick J. Wong" <djwong@kernel.org>
Signed-off-by: Pavel Reichl <preichl@redhat.com>