NFS: Fix misparsing of nfsv4 fs_locations attribute (take 2)

The changeset ea31a443 (nfs: Fix
misparsing of nfsv4 fs_locations attribute) causes the mountpath that is
calculated at the beginning of try_location() to be clobbered when we
later strncpy a non-nul terminated hostname using an incorrect buffer
length.

Signed-off-by: Trond Myklebust <Trond.Myklebust@netapp.com>