Removed a set NVIC priority call, added code to clear benign us timer timeout interrupt.

Author: linlingao

targets/TARGET_TI/TARGET_CC32XX/TARGET_CC3220SF/lp_ticker.c

@@ -52,8 +52,6 @@ void lp_ticker_init()
     }
     if (!rtc_inited) {
         NVIC_SetVector(INT_PRCM_IRQn, (uint32_t)lp_ticker_irq_handler);
-        // Set priority to highest 0
-        NVIC_SetPriority(INT_PRCM_IRQn, 0);
         NVIC_ClearPendingIRQ(INT_PRCM_IRQn);
         NVIC_EnableIRQ(INT_PRCM_IRQn);
         PRCMIntStatus(); // Read clears pending interrupts

targets/TARGET_TI/TARGET_CC32XX/TARGET_CC3220SF/us_ticker.c

@@ -56,7 +56,7 @@ void us_ticker_init(void)
         // Disable match interrupt. This is mbed OS requirement.
         TimerIntDisable(TIMERA0_BASE, TIMER_TIMA_MATCH);
         // Clear pending interrupt
-        TimerIntClear(TIMERA0_BASE, TIMER_TIMA_MATCH);
+        TimerIntClear(TIMERA0_BASE, TIMER_TIMA_MATCH | TIMER_TIMA_TIMEOUT);
     }
 }
 
@@ -80,7 +80,7 @@ void us_ticker_disable_interrupt(void)
 
 void us_ticker_clear_interrupt(void)
 {
-    TimerIntClear(TIMERA0_BASE, TIMER_TIMA_MATCH);
+    TimerIntClear(TIMERA0_BASE, TIMER_TIMA_MATCH | TIMER_TIMA_TIMEOUT);
 }
 
 void us_ticker_fire_interrupt(void)