closures: use seq_putc() in debug_show()

A single line break should be put into a sequence.  Thus use the
corresponding function "seq_putc".

This issue was transformed by using the Coccinelle software.

Link: https://lkml.kernel.org/r/e7faa2c4-9590-44b4-8669-69ef810277b1@web.de


Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Cc: Kent Overstreet <kent.overstreet@linux.dev>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>