i2c: s3c2410: Check clk_prepare_enable() return value

The clk_prepare_enable() function can fail so check the return
value and propagate the error in case of a failure.

Signed-off-by: Javier Martinez Canillas <javier@osg.samsung.com>
Reviewed-by: Krzysztof Kozlowski <k.kozlowski@samsung.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>