s390/entry: Make ret_from_fork() ready for lowcore relocation

In preparation of having lowcore at different address than zero,
add the base register to all lowcore accesses in ret_from_fork().

Reviewed-by: Heiko Carstens <hca@linux.ibm.com>
Signed-off-by: Sven Schnelle <svens@linux.ibm.com>
Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>

Author: svens-s390

arch/s390/kernel/entry.S

@@ -307,12 +307,13 @@ SYM_CODE_START(ret_from_fork)
 	lgr	%r3,%r11
 	brasl	%r14,__ret_from_fork
 	STACKLEAK_ERASE
-	lctlg	%c1,%c1,__LC_USER_ASCE
-	mvc	__LC_RETURN_PSW(16),STACK_FRAME_OVERHEAD+__PT_PSW(%r15)
+	GET_LC	%r13
+	lctlg	%c1,%c1,__LC_USER_ASCE(%r13)
+	mvc	__LC_RETURN_PSW(16,%r13),STACK_FRAME_OVERHEAD+__PT_PSW(%r15)
 	BPON
 	LBEAR	STACK_FRAME_OVERHEAD+__PT_LAST_BREAK(%r15)
+	stpt	__LC_EXIT_TIMER(%r13)
 	lmg	%r0,%r15,STACK_FRAME_OVERHEAD+__PT_R0(%r15)
-	stpt	__LC_EXIT_TIMER
 	LPSWEY	__LC_RETURN_PSW,__LC_RETURN_LPSWE
 SYM_CODE_END(ret_from_fork)