maxim: fix rtc if lp ticker not defined

lp ticker handler defined only if lp ticker is defined. In case not,
use only overflow, rtc0 not used.

targets/TARGET_Maxim/TARGET_MAX32600/rtc_api.c

@@ -33,6 +33,7 @@
 
 #include "rtc_api.h"
 #include "lp_ticker_api.h"
+#include "ticker_api.h"
 #include "cmsis.h"
 #include "rtc_regs.h"
 #include "pwrseq_regs.h"
@@ -73,8 +74,10 @@ void rtc_init(void)
     MXC_PWRSEQ->reg0 |= MXC_F_PWRSEQ_REG0_PWR_RTCEN_RUN;
 
     // Prepare interrupt handlers
+#ifdef DEVICE_LPTICKER
     NVIC_SetVector(RTC0_IRQn, (uint32_t)lp_ticker_irq_handler);
     NVIC_EnableIRQ(RTC0_IRQn);
+#endif
     NVIC_SetVector(RTC3_IRQn, (uint32_t)overflow_handler);
     NVIC_EnableIRQ(RTC3_IRQn);