clocksource: armada-370-xp: Get reference fixed-clock by name

The Armada XP timer has two mandatory clock inputs: nbclk and refclk,
as specified by the device-tree binding.

This commit fixes the clock selection. Instead of hard-coding the clock
rate for the 25 MHz reference fixed-clock, obtain the clock by its name.
Signed-off-by: Ezequiel Garcia <ezequiel.garcia@free-electrons.com>
Signed-off-by: Daniel Lezcano <daniel.lezcano@linaro.org>
Acked-by: Jason Cooper <jason@lakedaemon.net>
Acked-by: Gregory CLEMENT <gregory.clement@free-electrons.com>

drivers/clocksource/time-armada-370-xp.c

@@ -294,8 +294,11 @@ static void __init armada_370_xp_timer_common_init(struct device_node *np)
 
 static void __init armada_xp_timer_init(struct device_node *np)
 {
-	/* The fixed 25MHz timer is required, timer25Mhz is true by default */
-	timer_clk = 25000000;
+	struct clk *clk = of_clk_get_by_name(np, "fixed");
+
+	/* The 25Mhz fixed clock is mandatory, and must always be available */
+	BUG_ON(IS_ERR(clk));
+	timer_clk = clk_get_rate(clk);
 
 	armada_370_xp_timer_common_init(np);
 }