xen-pciback: Replace scnprintf() with sysfs_emit_at()

This is the third revision (v3) of this patch series.
No changes since v2—only adding Reviewed-by lines.

Reviewed-by: Juergen Gross <jgross@suse.com>
Signed-off-by: Ryan Chung <seokwoo.chung130@gmail.com>
Signed-off-by: Juergen Gross <jgross@suse.com>
Message-ID: <20250708001444.86155-1-seokwoo.chung130@gmail.com>