igb: Fix sparse warning about passing __beXX into leXX_to_cpup

We were casting the addr as __beXX and then passing it into le32_to_cpu
because the device expects the MAC address to be in network order even
though the register set is little endian.  Instead of casting it as __beXX
we can just cast it as __leXX in order to maintain consistency since the
region of memory is already in little endian order as far as we are
concerned.

Signed-off-by: Alexander Duyck <aduyck@mirantis.com>
Tested-by: Aaron Brown <aaron.f.brown@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>