i2c: designware: Use better constants from units.h

i2c: designware: Use better constants from units.h

When we use constants in a time or frequency related contexts,
it's better to utilise the respective definitions that have
encoded units in them. This will make code better to read and
understand.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Acked-by: Jarkko Nikula <jarkko.nikula@linux.intel.com>
Acked-by: Mukesh Kumar Savaliya <quic_msavaliy@quicinc.com>
Link: https://lore.kernel.org/r/20250416101702.2128740-1-andriy.shevchenko@linux.intel.com
Signed-off-by: Andi Shyti <andi.shyti@kernel.org>