net: dqs: use sysfs_emit() in favor of sprintf()

Commit 6025b913 ("net: dqs: add NIC stall detector based on BQL")
added three sysfs files.

Use the recommended sysfs_emit() helper.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Breno Leitao <leitao@debian.org>
Signed-off-by: David S. Miller <davem@davemloft.net>