checkpatch: switch indent allow plain return

It is a common and sane idiom to allow a single return on the end of a
case statement:

	switch (...) {
	case foo:	return bar;
	}

Add an exception for this.

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>