rnbd-clt: make rnbd_clt_change_capacity return void

No need to checking the return value, make it return void.

Acked-by: Jack Wang <jinpu.wang@ionos.com>
Signed-off-by: Guoqing Jiang <guoqing.jiang@linux.dev>
Link: https://lore.kernel.org/r/20220706133152.12058-9-guoqing.jiang@linux.dev


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