contrib/vhost-user-blk: fix overflowing expression

Coverity reported:

  >>>     CID 1549454:  Integer handling issues  (OVERFLOW_BEFORE_WIDEN)
  >>>     Potentially overflowing expression
          "le32_to_cpu(desc->num_sectors) << 9" with type "uint32_t"
          (32 bits, unsigned) is evaluated using 32-bit arithmetic, and
          then used in a context that expects an expression of type
          "uint64_t" (64 bits, unsigned).
  199                               le32_to_cpu(desc->num_sectors) << 9 };

Coverity noticed this issue after commit ab04420c3 ("contrib/vhost-user-*:
use QEMU bswap helper functions"), but it was pre-existing and introduced
from the beginning by commit caa1ee4313 ("vhost-user-blk: add
discard/write zeroes features support").

Explicitly cast the 32-bit value before the shift to fix this issue.

Fixes: Coverity CID 1549454
Fixes: 5ab04420c3 ("contrib/vhost-user-*: use QEMU bswap helper functions")
Fixes: caa1ee4313 ("vhost-user-blk: add discard/write zeroes features support")
Cc: changpeng.liu@intel.com
Suggested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Stefano Garzarella <sgarzare@redhat.com>
Message-Id: <20240712153857.207440-1-sgarzare@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Michael S. Tsirkin <mst@redhat.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>

contrib/vhost-user-blk/vhost-user-blk.c

@@ -196,7 +196,7 @@ vub_discard_write_zeroes(VubReq *req, struct iovec *iov, uint32_t iovcnt,
     VubDev *vdev_blk = req->vdev_blk;
     desc = buf;
     uint64_t range[2] = { le64_to_cpu(desc->sector) << 9,
-                          le32_to_cpu(desc->num_sectors) << 9 };
+                          (uint64_t)le32_to_cpu(desc->num_sectors) << 9 };
     if (type == VIRTIO_BLK_T_DISCARD) {
         if (ioctl(vdev_blk->blk_fd, BLKDISCARD, range) == 0) {
             g_free(buf);