ravb: remove erroneous comment

When addressing a review comment in a early version of the offending
patch a comment where left in which should have been removed. Remove the
comment to keep it consistent with the code.

Fixes: 75efa06f

 ("ravb: add support for changing MTU")
Reported-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Niklas Söderlund <niklas.soderlund+renesas@ragnatech.se>
Acked-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: David S. Miller <davem@davemloft.net>