ARM: EXYNOS4: Set appropriate I2C device variant

Set up a correct I2C bus controller variant name for Exynos4.
Without this change the I2C bus driver fails to acquire its
clocks.

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@samsung.com>
Signed-off-by: Kukjin Kim <kgene.kim@samsung.com>