bnx2x: fix byte-by-byte nvram write for BE machines

CC: Francious Romieu <romieu@fz.zoreil.com>
Signed-off-by: Dmitry Kravkov <dmitry@broadcom.com>
Signed-off-by: Eilon Greenstein <eilong@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>