taint: add missing comment

The description for 'D' was missing in the comment...  (causing me a
minute of WTF followed by looking at more of the code)

Signed-off-by: Arjan van de Ven <arjan@linux.intel.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>

kernel/panic.c

@@ -167,6 +167,7 @@ static const struct tnt tnts[] = {
  *  'M' - System experienced a machine check exception.
  *  'B' - System has hit bad_page.
  *  'U' - Userspace-defined naughtiness.
+ *  'D' - Kernel has oopsed before
  *  'A' - ACPI table overridden.
  *  'W' - Taint on warning.
  *  'C' - modules from drivers/staging are loaded.