checkpatch.pl: extend list of expected-to-be-const structures

Based on Arjan's suggestion, extend the list of ops structures that should
be const.

Signed-off-by: Emese Revfy <re.emese@gmail.com>
Cc: Andy Whitcroft <apw@shadowen.org>
Cc: Arjan van de Ven <arjan@infradead.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>