cleanup: Drop pointless return at end of function

A few functions now end with a label.  The next commit will clean them
up.

Signed-off-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-ID: <20250407082643.2310002-3-armbru@redhat.com>
[Straightforward conflict with commit 988ad4cceb (hw/loongarch/virt:
Fix cpuslot::cpu set at last in virt_cpu_plug()) resolved]

system/dirtylimit.c

@@ -337,8 +337,6 @@ static void dirtylimit_adjust_throttle(CPUState *cpu)
     if (!dirtylimit_done(quota, current)) {
         dirtylimit_set_throttle(cpu, quota, current);
     }
-
-    return;
 }
 
 void dirtylimit_process(void)