staging: ks7010_sdio: fix NULL pointer dereference and memory leak

priv is being explicitly dereferenced when it is still null, when
jumping to goto label err_free_netdev, before it is properly
updated with a valid memory address.

Also, when this happens, memory allocated for netdev at line 854:
netdev = alloc_etherdev(sizeof(*priv)) is not being free'd before
return, hence there is a memory leak.

The current code looks a bit too complicated and can be replaced
by just directly freeing netdev before return.

Notice that card->priv = NULL isn't required because the next thing
we do to card is kfree(card).

Addresses-Coverity-ID: 1467844 ("Explicit null dereferenced")
Suggested-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Gustavo A. R. Silva <gustavo@embeddedor.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>