i2c: exynos5: simplify transfer function

exynos5_i2c_xfer contains lots of dead code, let's remove it and simplify
the rest. The patch should not introduce functional changes.

Signed-off-by: Andrzej Hajda <a.hajda@samsung.com>
Suggested-by: Peter Rosin <peda@axentia.se>
Reviewed-by: Andi Shyti <andi@etezian.org>
Reviewed-by: Peter Rosin <peda@axentia.se>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>