phonet: phonet_device_get() fix

net/phonet/pn_dev.c: In function `phonet_device_get':
net/phonet/pn_dev.c:99: warning: 'dev' might be used uninitialized in this function

Signed-off-by: Eric Dumazet <eric.dumazet@gmail.com>
Acked-by: Rémi Denis-Courmont <remi.denis-courmont@nokia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>