checkpatch: conditional indent -- labels have different indent rules

Labels have different indent rules and must be ignored when checking the
conditional indent levels.  Also correct identify labels in single
statement conditionals.

Signed-off-by: Andy Whitcroft <apw@shadowen.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>