s390/mm: fix memory leak of ptlock in pmd_free_tlb

The pmd_free_tlb function fails to call pgtable_pmd_page_dtor.
Without the call the ptlock for the pmd tables will not be freed.
Add the missing call.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/tlb.h

@@ -121,6 +121,7 @@ static inline void pmd_free_tlb(struct mmu_gather *tlb, pmd_t *pmd,
 #ifdef CONFIG_64BIT
 	if (tlb->mm->context.asce_limit <= (1UL << 31))
 		return;
+	pgtable_pmd_page_dtor(virt_to_page(pmd));
 	tlb_remove_table(tlb, pmd);
 #endif
 }