arm: Correct signature for get_ticks()

This should be uint64_t to match its definition in common.h. Fix it.

Signed-off-by: Simon Glass <sjg@chromium.org>
diff --git a/arch/arm/cpu/armv8/generic_timer.c b/arch/arm/cpu/armv8/generic_timer.c
index cd92b2c..a2dda33 100644
--- a/arch/arm/cpu/armv8/generic_timer.c
+++ b/arch/arm/cpu/armv8/generic_timer.c
@@ -43,7 +43,7 @@
 	return cntpct;
 }
 
-unsigned long long get_ticks(void)
+uint64_t get_ticks(void)
 {
 	unsigned long ticks = timer_read_counter();