block: drop duplicated slice extension code

The current slice is extended when an I/O request exceeds the limit.
There is no need to extend the slice every time we check a request.
Signed-off-by: NStefan Hajnoczi <stefanha@redhat.com>
Tested-By: NBenoit Canet <benoit@irqsave.net>
Signed-off-by: NKevin Wolf <kwolf@redhat.com>

block.c

@@ -3867,10 +3867,7 @@ static bool bdrv_exceed_io_limits(BlockDriverState *bs, int nb_sectors,
     int      bps_ret, iops_ret;
 
     now = qemu_get_clock_ns(vm_clock);
-    if ((bs->slice_start < now)
-        && (bs->slice_end > now)) {
-        bs->slice_end = now + BLOCK_IO_SLICE_TIME;
-    } else {
+    if (now > bs->slice_end) {
         bs->slice_start = now;
         bs->slice_end   = now + BLOCK_IO_SLICE_TIME;
         memset(&bs->slice_submitted, 0, sizeof(bs->slice_submitted));