s390/mm: correct transfer of dirty & young bits in __pmd_to_pte

The dirty & young bit from the pmd is not copied correctly to the
pseudo pte in __pmd_to_pte. In fact it is not copied at all, the
bits get lost. As the old style huge page currently does not need
the dirty & young information this has no effect, but may be needed
in the future.

Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>