vmxnet3: remove unused variable

While doing some backporting I noticed that vmxnet3 had a variable that was set
but never used.  Get rid of it, and stop the compiler from griping

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: "VMware, Inc." <pv-drivers@vmware.com>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: Bhavesh Davda <bhavesh@vmware.com>
Signed-off-by: David S. Miller <davem@conan.davemloft.net>