i2c: viperboard: Use devm_kzalloc() functions

Use devm_kzalloc() functions to make cleanup paths simpler.

Signed-off-by: Jingoo Han <jg1.han@samsung.com>
Acked-by: Lars Poeschel <poeschel@lemonage.de>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>