fm10k: use ether_addr_copy to copy MAC address

Use the ether_addr_copy function instead of copying byte-by-byte in a
for-loop by hand.

Reported-by: Bruce Allan <bruce.w.allan@intel.com>
Signed-off-by: Jacob Keller <jacob.e.keller@intel.com>
Tested-by: Krishneil Singh <krishneil.k.singh@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>