The 'enable' clock of I2C master is required, we should return an error
if failed to get the 'enable' clock, to make sure the I2C driver can be
defer probe if the clock resource is not ready.
Signed-off-by: NBaolin Wang <baolin.wang@linaro.org>
Signed-off-by: NWolfram Sang <wsa@the-dreams.de>