nvme: don't pass cap to nvme_disable_ctrl

All seem to call it with ctrl->cap so no need to pass it
at all.

Reviewed-by: Minwoo Im <minwoo.im.dev@gmail.com>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Sagi Grimberg <sagi@grimberg.me>