UPSTREAM: selinux: check return value of sel_make_avc_files

sel_make_avc_files() might fail and return a negative errno value on
memory allocation failures. Re-add the check of the return value,
dropped in 66f8e2f03c02 ("selinux: sidtab reverse lookup hash table").

Reported by clang-analyzer:

    security/selinux/selinuxfs.c:2129:2: warning: Value stored to
      'ret' is never read [deadcode.DeadStores]
            ret = sel_make_avc_files(dentry);
            ^     ~~~~~~~~~~~~~~~~~~~~~~~~~~

Bug: 254441685
Fixes: 66f8e2f03c02 ("selinux: sidtab reverse lookup hash table")
Signed-off-by: Christian Göttsche <cgzones@googlemail.com>
Reviewed-by: Nick Desaulniers <ndesaulniers@google.com>
[PM: description line wrapping, added proper commit ref]
Signed-off-by: Paul Moore <paul@paul-moore.com>
(cherry picked from commit bcb62828e3e8c813b6613db6eb7fd9657db248fc)
Signed-off-by: Lee Jones <joneslee@google.com>
Change-Id: I9e125bee09b5d5ad5d053746a2cfb6ff0f57aced