isdn: clean up debug format string usage

Avoid unneeded local string buffers for constructing debug output.  Also
cleans up debug calls that contain a single parameter so that they cannot
be accidentally parsed as format strings.

Signed-off-by: Kees Cook <keescook@chromium.org>
Cc: Karsten Keil <isdn@linux-pingi.de>
Cc: David Miller <davem@davemloft.net>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: David S. Miller <davem@davemloft.net>