Fix a bug that I2C freq become fixed 100kHz

When I2C read/write, I2C freq ignores the setting of user and it become fixed 100kHz.
Implement change the freq according to the setting of user.
Fix a fear of bug that a static value will be indefiniteness.

There was a function that has the potential to be called with indefiniteness argument.
Modify to not call the function with indefiniteness argument.
Merge pull request #759 from masaohamanaka/master

Targets: RZ_A1H - Fix bugs that I2C freq become fixed 100kHz and a static value will be indefiniteness.