locking/lockdep: Simplify character output in seq_line()

Single characters should be put into a sequence.
Thus use the corresponding function “seq_putc” for one selected call.

This issue was transformed by using the Coccinelle software.

Suggested-by: Christophe Jaillet <christophe.jaillet@wanadoo.fr>
Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Signed-off-by: Boqun Feng <boqun.feng@gmail.com>
Link: https://lore.kernel.org/r/e346d688-7b01-462f-867c-ba52b7790d19@web.de