net: hns3: ensure media_type is unitialized

Media type is only set if h->ae_algo->ops->get_media_type is called
so there is a possibility that media_type is uninitialized when it is
used a switch statement.  Fix this by initializing media_type to
HNAE3_MEDIA_TYPE_UNKNOWN.

Detected by CoverityScan, CID#1452624("Uninitialized scalar variable")

Fixes: 496d03e9

 ("net: hns3: Add Ethtool support to HNS3 driver")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>