checkpatch: add missing WARN argument for min_t and max_t tests

The test for bad usage of min_t() and max_t() is missing the --ignore
type.  Add it.

Signed-off-by: Hui Zhu <teawater@gmail.com>
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>