s390/mm: handle asce-type exceptions as normal page fault

Git commit 9e34f2686bb088b211b6cac8772e1f644c6180f8
"s390/mm,tlb: tlb flush on page table upgrade fixup" removed the
exception handler for the asce-type exception. This is incorrect
as the user-copy with MVCOS can cause asce-type exceptions in
the kernel if a user pointer is too large. Those need to be
handled with do_no_context to branch to the fixup in the
user-copy code.

The simplest fix for this problem is to call do_dat_exception for
asce-type excpetions, as there is no vma for the address the code
will handle the exception correctly.
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/pgm_check.S

@@ -78,7 +78,7 @@ PGM_CHECK_DEFAULT			/* 34 */
 PGM_CHECK_DEFAULT			/* 35 */
 PGM_CHECK_DEFAULT			/* 36 */
 PGM_CHECK_DEFAULT			/* 37 */
-PGM_CHECK_DEFAULT			/* 38 */
+PGM_CHECK_64BIT(do_dat_exception)	/* 38 */
 PGM_CHECK_64BIT(do_dat_exception)	/* 39 */
 PGM_CHECK_64BIT(do_dat_exception)	/* 3a */
 PGM_CHECK_64BIT(do_dat_exception)	/* 3b */