checkpatch: square brackets -- exemption for array slices in braces

It is wholy reasonable to have square brackets representing array slices
in braces on the same line.  These should be spaced.

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>