MIPS: No need to check CPU 0 in {loongson3,bmips,octeon}_cpu_disable()

After commit 9cce844a ("MIPS: CPU#0 is not hotpluggable"),
c->hotpluggable is 0 for CPU 0 and it will not generate a control
file in sysfs for this CPU:

[root@linux loongson]# cat /sys/devices/system/cpu/cpu0/online
cat: /sys/devices/system/cpu/cpu0/online: No such file or directory
[root@linux loongson]# echo 0 > /sys/devices/system/cpu/cpu0/online
bash: /sys/devices/system/cpu/cpu0/online: Permission denied

So no need to check CPU 0 in {loongson3,bmips,octeon}_cpu_disable(),
just remove them.
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Acked-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/cavium-octeon/smp.c

@@ -290,9 +290,6 @@ static int octeon_cpu_disable(void)
 {
 	unsigned int cpu = smp_processor_id();
 
-	if (cpu == 0)
-		return -EBUSY;
-
 	if (!octeon_bootloader_entry_addr)
 		return -ENOTSUPP;
 

arch/mips/kernel/smp-bmips.c

@@ -362,9 +362,6 @@ static int bmips_cpu_disable(void)
 {
 	unsigned int cpu = smp_processor_id();
 
-	if (cpu == 0)
-		return -EBUSY;
-
 	pr_info("SMP: CPU%d is offline\n", cpu);
 
 	set_cpu_online(cpu, false);

arch/mips/loongson64/smp.c

@@ -544,9 +544,6 @@ static int loongson3_cpu_disable(void)
 	unsigned long flags;
 	unsigned int cpu = smp_processor_id();
 
-	if (cpu == 0)
-		return -EBUSY;
-
 	set_cpu_online(cpu, false);
 	calculate_cpu_foreign_map();
 	local_irq_save(flags);