net: qca_spi: Use SET_NETDEV_DEV()

Use SET_NETDEV_DEV() in qca_spi to create the "/sys/class/net/<if>/device"
symlink.

Signed-off-by: Stefan Wahren <stefan.wahren@i2se.com>
Signed-off-by: David S. Miller <davem@davemloft.net>