microblaze: timer: Do not initialized system timer twice

Only one system timer can be setup.
Do not initialize more system timers.
Signed-off-by: Michal Simek <michal.simek@xilinx.com>

arch/microblaze/kernel/timer.c

@@ -230,9 +230,15 @@ static int __init xilinx_clocksource_init(void)
 static void __init xilinx_timer_init(struct device_node *timer)
 {
 	struct clk *clk;
+	static int initialized;
 	u32 irq;
 	u32 timer_num = 1;
 
+	if (initialized)
+		return;
+
+	initialized = 1;
+
 	timer_baseaddr = of_iomap(timer, 0);
 	if (!timer_baseaddr) {
 		pr_err("ERROR: invalid timer base address\n");