tests/qtest: Fix npcm7xx_timer-test.c flaky test

npcm7xx_timer-test occasionally fails due to the state of the timers
from the previous test iteration.  Advancing the clock step after the
reset resolves this issue.

Fixes: https://gitlab.com/qemu-project/qemu/-/issues/1897
Signed-off-by: Chris Rauer <crauer@google.com>
Message-ID: <20230929000831.691559-1-crauer@google.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>

tests/qtest/npcm7xx_timer-test.c

@@ -465,6 +465,7 @@ static void test_periodic_interrupt(gconstpointer test_data)
     int i;
 
     tim_reset(td);
+    clock_step_next();
 
     tim_write_ticr(td, count);
     tim_write_tcsr(td, CEN | IE | MODE_PERIODIC | PRESCALE(ps));