checkpatch: reduce false positive rate of "complex macros"

Allow "#define foo struct.member" without bleating a warning.

This also allows "#define foo bar.baz->qux" and so on.

Signed-off-by: Joe Perches <joe@perches.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>