clk: keystone: Remove clk.h include

Clock provider drivers generally shouldn't include clk.h because
it's the consumer API. Remove the include here because this is a
provider driver.

Cc: Ivan Khoronzhuk <ivan.khoronzhuk@ti.com>
Cc: Murali Karicheri <m-karicheri2@ti.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>