smb: client: get rid of kstrdup() in get_ses_refpath()

After commit 36008fe6 ("smb: client: don't try following DFS links
in cifs_tree_connect()"), TCP_Server_Info::leaf_fullpath will no
longer be changed, so there is no need to kstrdup() it.

Signed-off-by: Paulo Alcantara (Red Hat) <pc@manguebit.com>
Signed-off-by: Steve French <stfrench@microsoft.com>