mm/slab: remove duplicate check in create_cache()

The WARN_ON() check in static function create_cache() is done by its only
parent __kmem_cache_create_args() before calling it.
	if (... ||
	    WARN_ON(... ||
		    object_size - args->usersize < args->useroffset))
		args->usersize = args->useroffset = 0;
	...
	s = create_cache(cache_name, object_size, args, flags);

Therefore, the WARN_ON() check in create_cache() can be safely removed.

Signed-off-by: Zhen Lei <thunder.leizhen@huawei.com>
Signed-off-by: Vlastimil Babka <vbabka@suse.cz>