nbd: use pr_err to output error message

nbd: use pr_err to output error message

Instead of using the long printk(KERN_ERR "nbd: ...") to
output error message, defining pr_fmt and using
the short pr_err("") to do that. The replacemen is done
by using the following command:

  sed -i 's/printk(KERN_ERR "nbd: /pr_err("/g' \
		  drivers/block/nbd.c

This patch also rewrap to 80 columns where possible.

Signed-off-by: Hou Tao <[email protected]>
Signed-off-by: Yu Kuai <[email protected]>
Reviewed-by: Josef Bacik <[email protected]>
Link: https://lore.kernel.org/r/[email protected]
Signed-off-by: Jens Axboe <[email protected]>