exynos: i2c: Fix i2c driver to handle NACKs properly

The Exynos5 i2c driver does not handle NACKs properly. This change:

- fixes the NACK processing problem (do not continue transaction if
  address cycle was NACKed)

- eliminates a fair amount of duplicate code

Signed-off-by: Vadim Bendebury <vbendeb@chromium.org>
Reviewed-by: Simon Glass <sjg@google.com>
Signed-off-by: Naveen Krishna Chatradhi <ch.naveen@samsung.com>