tests-mbed_hal-common_tickers: increase overflow protection limit

For NR51_DK US_TICKER_OV_LIMIT needs to be increased since if test is run few times in row sometimes fails. This is because NR51_DK is a slow board (16 MHz) with fast and short us ticker counter 1 MHz/16 bits.

TESTS/mbed_hal/common_tickers/main.cpp

@@ -40,7 +40,7 @@
 
 #define NUM_OF_CYCLES 100000
 
-#define US_TICKER_OV_LIMIT 20000
+#define US_TICKER_OV_LIMIT 35000
 #define LP_TICKER_OV_LIMIT 4000
 
 using namespace utest::v1;