liquidio: Replace vmalloc with kmalloc in octeon_register_dispatch_fn()

The size of struct octeon_dispatch is too small, it is better to use
kmalloc instead of vmalloc.

Suggested-by: Joe Perches <joe@perches.com>
Signed-off-by: Wang Hai <wanghai38@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>