i2c: designware: remove HAVE_CLK build dependecy

Since 93abe8e4 (clk: add non CONFIG_HAVE_CLK routines) code using clk.h
like this platform driver need not depend on HAVE_CLK. Also, remove a
redundant clk.h include from core driver.

Signed-off-by: Baruch Siach <baruch@tkos.co.il>
Signed-off-by: Wolfram Sang <wsa@the-dreams.de>