tests/periph_timer_periodic: lower CYCLE_MS

Reduce CYCLE_MS to 25 ms so the period also fits into a 16 bit 1 MHz
timer.

tests/periph_timer_periodic/main.c

@@ -38,7 +38,7 @@
  * provides a configuration for it.
  */
 #define TIMER_CYCL  XTIMER_DEV
-#define CYCLE_MS    100UL
+#define CYCLE_MS    25UL
 #define CYCLES_MAX   10
 
 static unsigned count[TIMER_CHANNEL_NUMOF];

tests/periph_timer_periodic/tests/01-run.py

@@ -16,9 +16,9 @@ def testfunc(child):
     start = time.time()
     child.expect_exact('TEST SUCCEEDED')
     end = time.time()
-    # test should run 10 cycles with 100ms each
-    assert (end - start) > 1
-    assert (end - start) < 1.5
+    # test should run 10 cycles with 25ms each
+    assert (end - start) > 0.25
+    assert (end - start) < 0.35
 
 
 if __name__ == "__main__":