MIPS: Loongson64: Make some functions static in smp.c

Make some functions static to fix the following sparse warnings:

  arch/mips/loongson64/smp.c:54:5: sparse: sparse: symbol 'ipi_read_clear' was not declared. Should it be static?
  arch/mips/loongson64/smp.c:55:6: sparse: sparse: symbol 'ipi_write_action' was not declared. Should it be static?
  arch/mips/loongson64/smp.c:56:6: sparse: sparse: symbol 'ipi_write_enable' was not declared. Should it be static?
  arch/mips/loongson64/smp.c:57:6: sparse: sparse: symbol 'ipi_clear_buf' was not declared. Should it be static?
  arch/mips/loongson64/smp.c:58:6: sparse: sparse: symbol 'ipi_write_buf' was not declared. Should it be static?

Fixes: fed4955f ("MIPS: Loongson64: Add Mail_Send support for 3A4000+ CPU")
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Tiezhu Yang <yangtiezhu@loongson.cn>
Signed-off-by: Thomas Bogendoerfer <tsbogend@alpha.franken.de>

arch/mips/loongson64/smp.c

@@ -51,11 +51,11 @@ static uint32_t core0_c0count[NR_CPUS];
 		__wbflush();			\
 	} while (0)
 
-u32 (*ipi_read_clear)(int cpu);
-void (*ipi_write_action)(int cpu, u32 action);
-void (*ipi_write_enable)(int cpu);
-void (*ipi_clear_buf)(int cpu);
-void (*ipi_write_buf)(int cpu, struct task_struct *idle);
+static u32 (*ipi_read_clear)(int cpu);
+static void (*ipi_write_action)(int cpu, u32 action);
+static void (*ipi_write_enable)(int cpu);
+static void (*ipi_clear_buf)(int cpu);
+static void (*ipi_write_buf)(int cpu, struct task_struct *idle);
 
 /* send mail via Mail_Send register for 3A4000+ CPU */
 static void csr_mail_send(uint64_t data, int cpu, int mailbox)