octeon_ep: add missing destroy_workqueue in octep_init_module

octep_init_module misses destroy_workqueue in error path,
this patch fixes that.

Fixes: 862cd659 ("octeon_ep: Add driver framework and device initialization")
Signed-off-by: Zheng Bin <zhengbin13@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>