[realtek] Force EEPROM CS low before disabling EEPROM access mode

[realtek] Force EEPROM CS low before disabling EEPROM access mode

Some RTL8169 cards seem to drive the EEPROM CS line high (i.e. active)
when 9346CR.EEM is set to "normal operating mode", with the result
that the CS line is never deasserted.  The symptom of this is that the
first read from the EEPROM will work, while all subsequent reads will
return garbage data.

Reported-by: Thomas Miletich <thomas.miletich@gmail.com>
Debugged-by: Thomas Miletich <thomas.miletich@gmail.com>
Tested-by: Thomas Miletich <thomas.miletich@gmail.com>
Signed-off-by: Michael Brown <mcb30@ipxe.org>