ice: small efficiency fixes

Add a small bit of efficiency to the code by adding a
prefetch of the port_info structure in order to help
avoid a cache miss a little later on in execution.

Also add an unlikely statement to a branch which
generally will never happen in normal operation.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Andrew Bowers <andrewx.bowers@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>