Fix eeprom flags for eeprom build

Fix eeprom flags for eeprom build

Original mail on libftdi mailinglist:
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   Hello,

the eeprom_decode function sets struct ftdi_eeprom flags like this:
   eeprom->self_powered = buf[0x08] & 0x40;
but the eeprom_build uses the flags this way:
   if (eeprom->self_powered == 1)
as the result the bits won't be set. I suggest the patch below.

   - Jarkko Sonninen