subst: Fix free of uninit pointers

subst: Fix free of uninit pointers

in add_subst(), if the malloc of ent->name fails, we goto fail;
which will free ent->name (which is null, so OK) but also free
ent->value (which is uninitialized).  There is no case where
we must free ent->value on an error (it is allocated last, and
if it fails it of course doesn't need to be freed) so just
remove it.

Also "retval" is only assigned once to the constant ENOMEM,
so we can just return that explicitly in the failure case.

Signed-off-by: Eric Saneeen <sandeen@redhat.com>
Signed-off-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>