net/e1000: Fix EEPROM access error

Commit 95186063 may have changed
the logic unintentially from "if (!(swfw_sync & (fwmask | swmask)))"
to "if ((swfw_sync & swmask) && !(swfw_sync & fwmask))". This change
breaks some e1000 NIC with a message "ERROR: Unable to read EEPROM!".

Signed-off-by: York Sun <yorksun@freescale.com>
CC: Marek Vasut <marex@denx.de>
CC: Tim Harvey <tharvey@gateworks.com>
Acked-by: Marcel Ziswiler <marcel@ziswiler.com>