dynamic_debug: replace strcpy with strlcpy, in ddebug_setup_query()

Replace strcpy with strlcpy, and add define for the size constant.

[jbaron@redhat.com: Use DDEBUG_STRING_SIZE for overflow check]
Signed-off-by: Jim Cromie <jim.cromie@gmail.com>
Signed-off-by: Jason Baron <jbaron@redhat.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>