nrf52; fix build when no 32k defines are set.
@@ -67,7 +67,10 @@ hal_debugger_connected(void)
void
hal_system_clock_start(void)
{
+#if MYNEWT_VAL(XTAL_32768) || MYNEWT_VAL(XTAL_RC) || \
+ MYNEWT_VAL(XTAL_32768_SYNTH)
uint32_t mask;
+#endif
#if MYNEWT_VAL(XTAL_32768)
/* Check if this clock source is already running */
