caif: remove unneeded variable from caif_net_open()

We don't use the "ser" variable so I've removed it.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Acked-by: Sjur Braendeland <sjur.brandeland@stericsson.com>
Signed-off-by: David S. Miller <davem@davemloft.net>