s390/mm: fix pmd_pfn() for thp

The pfn calculation in pmd_pfn() is broken for thp, because it uses
HPAGE_SHIFT instead of the normal PAGE_SHIFT. This is fixed by removing
the distinction between thp and normal pmds in that function, and always
using PAGE_SHIFT.
Reported-by: Christian Borntraeger <borntraeger@de.ibm.com>
Signed-off-by: Gerald Schaefer <gerald.schaefer@de.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/include/asm/pgtable.h

@@ -1387,10 +1387,7 @@ static inline int has_transparent_hugepage(void)
 
 static inline unsigned long pmd_pfn(pmd_t pmd)
 {
-	if (pmd_trans_huge(pmd))
-		return pmd_val(pmd) >> HPAGE_SHIFT;
-	else
-		return pmd_val(pmd) >> PAGE_SHIFT;
+	return pmd_val(pmd) >> PAGE_SHIFT;
 }
 #endif /* CONFIG_TRANSPARENT_HUGEPAGE */