e1000e: use correct pointer when memcpy'ing a 2-dimensional array

*e1000_gstrings_test is not the same size as e1000_gstrings_test.

Signed-off-by: Bruce Allan <bruce.w.allan@intel.com>
Tested-by: Jeff Pieper <jeffrey.e.pieper@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>