Remove unnecessary break statements

Fix these warnings from cppcheck:

hw/display/cirrus_vga.c:2603:
hw/sd/sd.c:348:
hw/timer/exynos4210_mct.c:1033:
target-arm/translate.c:9886:
target-s390x/mem_helper.c:518:
target-unicore32/translate.c:1936:
 style: Consecutive return, break, continue, goto or throw statements are unnecessary.

Signed-off-by: Stefan Weil <sw@weilnetz.de>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Andreas Färber <afaerber@suse.de>
Signed-off-by: Michael Tokarev <mjt@tls.msk.ru>

hw/timer/exynos4210_mct.c

@@ -1030,7 +1030,6 @@ static uint64_t exynos4210_mct_read(void *opaque, hwaddr offset,
     case G_INT_ENB:
         value = s->g_timer.reg.int_enb;
         break;
-        break;
     case G_WSTAT:
         value = s->g_timer.reg.wstat;
         break;