igb/igc: use strongly typed pointer

The igb and igc driver both use a trick of creating a local type
pointer on the stack to ease dealing with a receive descriptor in
64 bit chunks for printing.  Sparse however was not taken into
account and receive descriptors are always in little endian
order, so just make the unions use __le64 instead of u64.

No functional change.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
Tested-by: Dvora Fuxbrumer <dvorax.fuxbrumer@linux.intel.com>
Tested-by: Dave Switzer <david.switzer@intel.com>
Signed-off-by: Tony Nguyen <anthony.l.nguyen@intel.com>