s390/entry: Use lay instead of aghik

s390/entry: Use lay instead of aghik

Use the lay instruction instead of aghik. aghik is only available since
z196, therefore compiling the kernel for z10 results in this error:

   arch/s390/kernel/entry.S: Assembler messages:
   arch/s390/kernel/entry.S:165: Error: Unrecognized opcode: `aghik'

Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511261518.nBbQN5h7-lkp@intel.com/
Fixes: f5730d44e05e ("s390: Add stackprotector support")
Reviewed-by: Jan Polensky <japo@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>