ARM: Tegra: Seaboard: Fix I2C bus numbering for ADT7461

Bus number 4 doesn't exist in the mainline kernel. The device is
attached to bus number 3. (In the ChromeOS kernel, one of the I2C
busses is split in two with a mux, this pushing all later busses
to a higher bus number. In this case, 4 is the correct bus number
for the ADT7461).

Signed-off-by: Stephen Warren <swarren@nvidia.com>
Signed-off-by: Arnd Bergmann <arnd@arndb.de>