[MIPS] Check function pointers are non-zero before calling.
    
Several boards don't initialize the pointers, so let's play safe.
    
Signed-off-by: Ralf Baechle <ralf@linux-mips.org>
diff --git a/arch/mips/kernel/reset.c b/arch/mips/kernel/reset.c
index ae2ba67..a131aa0c 100644
--- a/arch/mips/kernel/reset.c
+++ b/arch/mips/kernel/reset.c
@@ -23,16 +23,18 @@
 
 void machine_restart(char *command)
 {
-	_machine_restart(command);
+	if (_machine_restart)
+		_machine_restart(command);
 }
 
 void machine_halt(void)
 {
-	_machine_halt();
+	if (_machine_halt)
+		_machine_halt();
 }
 
 void machine_power_off(void)
 {
-	_machine_power_off();
+	if (_machine_power_off)
+		_machine_power_off();
 }
-