checkpatch: complex macro should allow the empty do while loop

It is common to stub out a function as below, this is triggering a complex
macro format incorrectly.  Sort this out:

    #define cma_early_regions_reserve(reserve)   do { } while (0)

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