MIPS: Loongson64: Add WARN_ON on kexec related kmalloc failed

Add WARN_ON on kexec related kmalloc failed, avoid to pass NULL pointer
to following memcpy and loongson_kexec_prepare.

Fixes: 6ce4889 ("MIPS: Loongson64: Add kexec/kdump support")
Signed-off-by: Liao Chang <liaochang1@huawei.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/loongson64/reset.c

@@ -16,6 +16,7 @@
 #include <asm/bootinfo.h>
 #include <asm/idle.h>
 #include <asm/reboot.h>
+#include <asm/bug.h>
 
 #include <loongson.h>
 #include <boot_param.h>
@@ -159,8 +160,17 @@ static int __init mips_reboot_setup(void)
 
 #ifdef CONFIG_KEXEC
 	kexec_argv = kmalloc(KEXEC_ARGV_SIZE, GFP_KERNEL);
+	if (WARN_ON(!kexec_argv))
+		return -ENOMEM;
+
 	kdump_argv = kmalloc(KEXEC_ARGV_SIZE, GFP_KERNEL);
+	if (WARN_ON(!kdump_argv))
+		return -ENOMEM;
+
 	kexec_envp = kmalloc(KEXEC_ENVP_SIZE, GFP_KERNEL);
+	if (WARN_ON(!kexec_envp))
+		return -ENOMEM;
+
 	fw_arg1 = KEXEC_ARGV_ADDR;
 	memcpy(kexec_envp, (void *)fw_arg2, KEXEC_ENVP_SIZE);