dyndbg: use seq_putc() in ddebug_proc_show()

Single characters 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/375b5b4b-6295-419e-bae9-da724a7a682d@web.de


Signed-off-by: Markus Elfring <elfring@users.sourceforge.net>
Cc: Jason Baron <jbaron@akamai.com>
Cc: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>