net: hns3: minor cleanup in hns3_clean_rx_ring

The unused_count variable is used to indicate how many
RX BD need attaching new buffer in hns3_clean_rx_ring,
and the clean_count variable has the similar meaning.

This patch removes the clean_count variable and use
unused_count to uniformly indicate the RX BD that need
attaching new buffer.

This patch also clean up some coding style related to
variable assignment in hns3_clean_rx_ring.

Signed-off-by: Yunsheng Lin <linyunsheng@huawei.com>
Reviewed-by: Peng Li <lipeng321@huawei.com>
Signed-off-by: Huazhong Tan <tanhuazhong@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>