ARM: dts: aspeed: Rainier: Fix humidity sensor bus address

The si7021 was incorrectly placed at 0x20 on i2c bus 7. It is at 0x40.

Fixes: 9c44db70 ("ARM: dts: aspeed: rainier: Add i2c devices")
Signed-off-by: Eddie James <eajames@linux.ibm.com>
Reviewed-by: Joel Stanley <joel@jms.id.au>
Signed-off-by: Joel Stanley <joel@jms.id.au>