s390: correct some inline assembly constraints

Inline assembly code changed in this patch should really use "Q"
constraint "Memory reference without index register and with short
displacement". The kernel build with kasan instrumentation enabled
might occasionally break otherwise (due to stack instrumentation).

Signed-off-by: Vasily Gorbik <gor@linux.ibm.com>
Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com>