s390/suspend: fix stack setup in swsusp_arch_suspend

The patch that added support for the virtually mapped kernel stacks changed
swsusp_arch_suspend to switch to the nodat-stack as the vmap stack is not
available while going in and out of suspend.

Unfortunately the switch to the nodat-stack is incorrect which breaks
suspend to disk.

Cc: stable@vger.kernel.org # v4.20
Fixes: ce3dc44 ("s390: add support for virtually mapped kernel stacks")
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>

arch/s390/kernel/swsusp.S

@@ -30,10 +30,10 @@
 	.section .text
 ENTRY(swsusp_arch_suspend)
 	lg	%r1,__LC_NODAT_STACK
-	aghi	%r1,-STACK_FRAME_OVERHEAD
 	stmg	%r6,%r15,__SF_GPRS(%r1)
+	aghi	%r1,-STACK_FRAME_OVERHEAD
 	stg	%r15,__SF_BACKCHAIN(%r1)
-	lgr	%r1,%r15
+	lgr	%r15,%r1
 
 	/* Store FPU registers */
 	brasl	%r14,save_fpu_regs