ice: Fix return value from NAPI poll

ice_napi_poll is hard-coded to return zero when it's done. It should
instead return the work done (if any work was done). The only time it
should return zero is if an interrupt or poll is handled and no work
is performed. So change the return value to be the minimum of work
done or budget-1.

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