PXA: Fix missing get_tbclk() breaking vpac boards

Signed-off-by: Marek Vasut <marek.vasut@gmail.com>
diff --git a/arch/arm/cpu/pxa/timer.c b/arch/arm/cpu/pxa/timer.c
index b7b0da9..a8f7462 100644
--- a/arch/arm/cpu/pxa/timer.c
+++ b/arch/arm/cpu/pxa/timer.c
@@ -94,3 +94,8 @@
 	while (get_ticks() < tmp)	/* loop till event */
 		 /*NOP*/;
 }
+
+ulong get_tbclk(void)
+{
+	return TIMER_FREQ_HZ;
+}