powerpc/64e: Fix wrong test in __ptep_test_and_clear_young()

Commit 45201c87 ("powerpc/nohash: Remove hash related code from
nohash headers.") replaced:

  if ((pte_val(*ptep) & (_PAGE_ACCESSED | _PAGE_HASHPTE)) == 0)
	return 0;

By:

  if (pte_young(*ptep))
	return 0;

But it should be:

  if (!pte_young(*ptep))
	return 0;

Fix it.

Fixes: 45201c87 ("powerpc/nohash: Remove hash related code from nohash headers.")
Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://msgid.link/8bb7f06494e21adada724ede47a4c3d97e879d40.1695659959.git.christophe.leroy@csgroup.eu