e1000e: Use sizeof struct rather than pointer in e1000_get_eeprom()

Don't use the sizeof the pointer to clear the result

Signed-off-by: Roel Kluin <roel.kluin@gmail.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>