ps3disk: add error handling support for add_disk()

We never checked for errors on add_disk() as this function
returned void. Now that this is fixed, use the shiny new
error handling.

Signed-off-by: Luis Chamberlain <mcgrof@kernel.org>
Tested-by: Geoff Levand <geoff@infradead.org>
Link: https://lore.kernel.org/r/20211015235219.2191207-11-mcgrof@kernel.org


Signed-off-by: Jens Axboe <axboe@kernel.dk>