ice: Correctly handle return values for init DCB

In the init path for DCB, the call to ice_init_dcb()
can return a non-zero value for either an actual
error, or due to the FW lldp engine being stopped.

We are currently treating all non-zero values only as
an indication that the FW LLDP engine is stopped.

Check for an actual error in the DCB init flow.

Signed-off-by: Dave Ertman <david.m.ertman@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>