ravb: kill useless *switch* defaults

The  driver has the *default* case doing nothing in the *switch* statement
with an integer expression -- remove it.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Reviewed-by: Simon Horman <horms+renesas@verge.net.au>
Signed-off-by: David S. Miller <davem@davemloft.net>