Include us_ticker.h in scheduler implementation.

Author: niklarm

frameworks\utest/source/shim.cpp

@@ -54,6 +54,11 @@ utest_v1_scheduler_t utest_v1_get_scheduler()
 }
 
 #elif UTEST_SHIM_SCHEDULER_USE_US_TICKER
+#ifdef YOTTA_MBED_HAL_VERSION_STRING
+#   include "mbed-hal/us_ticker.h"
+#else
+#   include "us_ticker.h"
+#endif
 // only one callback is active at any given time
 static volatile utest_v1_harness_callback_t minimal_callback;
 static volatile utest_v1_harness_callback_t ticker_callback;