block/rnbd: Use sysfs_emit instead of s*printf function for sysfs show

block/rnbd: Use sysfs_emit instead of s*printf function for sysfs show

sysfs_emit function was added to be aware of the PAGE_SIZE maximum of
the temporary buffer used for outputting sysfs content, so there is no
possible overruns. So replace the uses of any s*printf functions for
the sysfs show functions with sysfs_emit.

Signed-off-by: Md Haris Iqbal <haris.iqbal@ionos.com>
Signed-off-by: Jack Wang <jinpu.wang@ionos.com>
Link: https://lore.kernel.org/r/20210726115950.470543-3-jinpu.wang@ionos.com
Signed-off-by: Jens Axboe <axboe@kernel.dk>