I2C: add wait time after write to let EEPROM write

The Atmel AT24C02 defines a maximum tWR waiting time after a byte
write of 5 ms before a next write.
Enforcing this wait time also fixed the failed verification in qmod,
where it was reading 0xffff instead of the written value.

Change-Id: I42c90b8d0329e425f275067e87d584212a43a90b

firmware/libboard/qmod/source/i2c.c

@@ -185,6 +185,8 @@ int eeprom_write_byte(uint8_t slave, uint8_t addr, uint8_t byte)
 	nack = i2c_write_byte(false, true, byte);
 	if (nack)
 		goto out_stop;
+	/* Wait tWR time to ensure EEPROM is writing correctly (tWR = 5 ms for AT24C02) */
+	mdelay(5);
 
 out_stop:
 	i2c_stop_cond();