i2c: designware-baytrail: describe magic numbers

The patch converts hardcoded numerical constants to a named ones.

While here, align the variable name in get_sem() and reset_semaphore().

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: David E. Box <david.e.box@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>