LoongArch: Fix build errors for CONFIG_RANDSTRUCT

When CONFIG_RANDSTRUCT enabled, members of task_struct are randomized.
There is a chance that TASK_STACK_CANARY be out of 12bit immediate's
range and causes build errors. TASK_STACK_CANARY is naturally aligned,
so fix it by replacing ld.d/st.d with ldptr.d/stptr.d which have 14bit
immediates.

Cc: stable@vger.kernel.org
Reported-by: kernel test robot <lkp@intel.com>
Closes: https://lore.kernel.org/oe-kbuild-all/202511240656.0NaPcJs1-lkp@intel.com/
Suggested-by: Rui Wang <wangrui@loongson.cn>
Signed-off-by: Huacai Chen <chenhuacai@loongson.cn>

Author: chenhuacai

arch/loongarch/kernel/switch.S

@@ -25,8 +25,8 @@ SYM_FUNC_START(__switch_to)
 	stptr.d a4, a0, THREAD_SCHED_CFA
 #if defined(CONFIG_STACKPROTECTOR) && !defined(CONFIG_SMP)
 	la	t7, __stack_chk_guard
-	LONG_L	t8, a1, TASK_STACK_CANARY
-	LONG_S	t8, t7, 0
+	ldptr.d	t8, a1, TASK_STACK_CANARY
+	stptr.d	t8, t7, 0
 #endif
 	move	tp, a2
 	cpu_restore_nonscratch a1