Add the clear process of "inited" flag in lp_ticker_free()

I added "lp_ticker_inited = 0" in lp_ticker_free() of lp_ticker.c, so
re-initialization will work.

Author: TomoYamanaka

targets/TARGET_RENESAS/TARGET_RZ_A1XX/lp_ticker.c

@@ -79,6 +79,7 @@ void lp_ticker_free(void)
     GIC_ClearPendingIRQ(LP_TICKER_TIMER_IRQn);
 
     MTU2TIER  &= ~MTU2_TIER_n_TGIEA;
+    lp_ticker_inited = 0;
     mtu2_free();
 }