i2c: designware: Use DIV_ROUND_CLOSEST() macro

[ Upstream commit c045214a ]

Instead of open-coding DIV_ROUND_CLOSEST() and similar use the macros directly.
While at it, replace numbers with predefined SI metric prefixes.

No functional change intended.

Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Wolfram Sang <wsa@kernel.org>
Stable-dep-of: c8c37bc5 ("i2c: designware: use casting of u64 in clock multiplication to avoid overflow")
Signed-off-by: Sasha Levin <sashal@kernel.org>