i2c: au1550: Convert to devm_kzalloc and devm_ioremap_resource

Use devm_* APIs to simplify the code.

Signed-off-by: Axel Lin <axel.lin@ingics.com>
Tested-by: Manuel Lauss <manuel.lauss@gmail.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>