dm-ebs: fix incorrect device offset check in ebs_ctr()

<offset> is a backing-device sector offset; ti->len is the virtual
target length. Comparing them rejects valid tables, e.g.:

  dmsetup create ebs0 --table "0 1048576 ebs /dev/sda 2097152 1 8"
  -> ebs: Invalid device offset sector (-EINVAL)

Drop the check. Bounds against the backing device are already
enforced later by device_area_is_invalid() via ebs_iterate_devices().

Cc: stable@vger.kernel.org
Fixes: d3c7b35c20d6 ("dm: add emulated block size target")
Signed-off-by: Genjian Zhang <zhanggenjian@kylinos.cn>
Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>