block/file-posix: fix workaround in raw_do_pwrite_zeroes()

We should not set overlap_bytes:

1. Don't worry: it is calculated by bdrv_mark_request_serialising() and
   will be equal to or greater than bytes anyway.

2. If the request was already aligned up to some greater alignment,
   than we may break things: we reduce overlap_bytes, and further
   bdrv_mark_request_serialising() may not help, as it will not restore
   old bigger alignment.

Signed-off-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com>
Message-Id: <20201203222713.13507-2-vsementsov@virtuozzo.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>

block/file-posix.c

@@ -2952,7 +2952,6 @@ raw_do_pwrite_zeroes(BlockDriverState *bs, int64_t offset, int bytes,
 
         end = INT64_MAX & -(uint64_t)bs->bl.request_alignment;
         req->bytes = end - req->offset;
-        req->overlap_bytes = req->bytes;
 
         bdrv_mark_request_serialising(req, bs->bl.request_alignment);
     }