doc: Fix sanitize command examples as character device

doc: Fix sanitize command examples as character device

The documentation for nvme-sanitize provides conflicting statements

Specifically, the documentation says:

    The parameter is mandatory NVMe character device (ex: /dev/nvme0)

However, in the EXAMPLES section, the syntax shown references the Block device:

    nvme sanitize /dev/nvme0n1 --sanact=0x01

Using the characther device is the correct device, thus update the example
accordingly.

Signed-off-by: Tokunori Ikegami <ikegami.t@gmail.com>
[dwagner: added commit message]
Signed-off-by: Daniel Wagner <dwagner@suse.de>