fhci-hub: kill 'len' variable in fhci_hub_control()

The 'len' variable in fhci_hub_control() is write-only, so totally useless.

Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>