Increase ticker test time for slower devices

Increase the hal ticker test time from 30s to 60s to prevent
a timeout from occurring on slower devices, such as the nrf51.

Author: c1728p9

TESTS/mbed_hal/ticker/main.cpp

@@ -2367,7 +2367,7 @@ static const case_t cases[] = {
 
 static utest::v1::status_t greentea_test_setup(const size_t number_of_cases)
 {
-    GREENTEA_SETUP(30, "default_auto");
+    GREENTEA_SETUP(60, "default_auto");
     return verbose_test_setup_handler(number_of_cases);
 }