ixgbe: Only clear adapter_stopped if ixgbe_setup_fc succeeded

A logic error here results in the adapter_stopped flag only being
cleared when ixgbe_setup_fc returns an error. Correct the logic.

Signed-off-by: Mark Rustad <mark.d.rustad@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>