[nfs] Fix an invalid free() when loading a regular (non-symlink) file

An invalid free() was ironically introduced by fixing another invalid
free in commit 7aa69c4 ("[nfs] Fix an invalid free() when loading a
symlink").

Signed-off-by: Marin Hannache <git@mareo.fr>
Signed-off-by: Michael Brown <mcb30@ipxe.org>