[cm3] fix doxygen for systick_get_value, add systick_get_reload

Fix the reload value in the examples:
to get a SysTick interrupt every N clock pulses: set reload to N-1
see http://infocenter.arm.com/help/topic/com.arm.doc.dui0552a/BGBEEJHC.html#BABGACGG

lib/cm3/systick.c

@@ -60,9 +60,20 @@ void systick_set_reload(u32 value)
 @returns 24 bit reload value as u32.
 */
 
+u32 systick_get_reload(void)
+{
+	return (STK_LOAD & 0x00FFFFFF);
+}
+
+/*-----------------------------------------------------------------------------*/
+/** @brief Get the current SysTick counter value.
+
+@returns 24 bit current value as u32.
+*/
+
 u32 systick_get_value(void)
 {
-	return STK_VAL;
+	return (STK_VAL & 0x00FFFFFF);
 }
 
 /*-----------------------------------------------------------------------------*/