checkpatch: ensure we do not collapse bracketed sections into constants

When determining if a return () sequence is a function style bracketing we
simplify the expression one bracket at a time replacing each with a
constant.  However this can trigger a false merge with expressions as
below:

	return (foo)0;

Prevent this false merging.

Reported-by: Hitoshi Mitake <mitake@dcl.info.waseda.ac.jp>
Signed-off-by: Andy Whitcroft <apw@canonical.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>