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: f5730d4 ("s390: Add stackprotector support")
Reviewed-by: Jan Polensky <japo@linux.ibm.com>
Signed-off-by: Heiko Carstens <hca@linux.ibm.com>

Author: hcahca

arch/s390/kernel/entry.S

@@ -162,7 +162,7 @@ SYM_FUNC_START(__switch_to_asm)
 	stg	%r3,__LC_CURRENT(%r13)		# store task struct of next
 	stg	%r15,__LC_KERNEL_STACK(%r13)	# store end of kernel stack
 	lg	%r15,__THREAD_ksp(%r1,%r3)	# load kernel stack of next
-	aghik	%r4,%r3,__TASK_pid
+	lay	%r4,__TASK_pid(%r3)
 	mvc	__LC_CURRENT_PID(4,%r13),0(%r4) # store pid of next
 	ALTERNATIVE "nop", "lpp _LPP_OFFSET(%r13)", ALT_FACILITY(40)
 #ifdef CONFIG_STACKPROTECTOR