qed: Fix static checker warning.

Smatch compains about qed_roce_ll2_tx() dereference
of the 'cdev' variable while testing its validity later.
As the validation checking is an over-kill [variable would always
be set], simply remove it.

Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Fixes: abd49676 ("qed: Add RoCE ll2 & GSI support")
Signed-off-by: Yuval Mintz <Yuval.Mintz@caviumnetworks.com>
Signed-off-by: David S. Miller <davem@davemloft.net>