i2c: mvtwsi: Swab the register address if its size is > 1

i2c: mvtwsi: Swab the register address if its size is > 1

Testing on Armada XP with an EEPROM using register address with size
of 2 has shown, that the register address bytes are sent to the I2C
EEPROM in the incorrect order. This patch swabs the address bytes so
that the correct address is transferred to the I2C device.

BTW: This worked without any issues before migrating Armada XP to
DM I2C.

Signed-off-by: Stefan Roese <sr@denx.de>
Cc: Heiko Schocher <hs@denx.de>
Cc: Samuel Holland <samuel@sholland.org>
Cc: Baruch Siach <baruch@tkos.co.il>
Cc: Pali Rohár <pali@kernel.org>
Cc: Marek Behún <marek.behun@nic.cz>
Tested-by: Marek Behún <marek.behun@nic.cz>