sfc: use sysfs_emit() to instead of scnprintf()

sfc: use sysfs_emit() to instead of scnprintf()

Follow the advice of the Documentation/filesystems/sysfs.rst and show()
should only use sysfs_emit() or sysfs_emit_at() when formatting the
value to be returned to user space.

Signed-off-by: ye xingchen <ye.xingchen@zte.com.cn>
Reviewed-by: Leon Romanovsky <leonro@nvidia.com>
Acked-by: Martin Habets <habetsm.xilinx@gmail.com>
Link: https://lore.kernel.org/r/202212051021451139126@zte.com.cn
Signed-off-by: Jakub Kicinski <kuba@kernel.org>