clk: Make x86/ conditional on CONFIG_COMMON_CLK

Fix Makefile for x86 support, dependency on CONFIG_COMMON_CLK
was not explicit

Fixes: 701190fd ('clk: x86: add support for Lynxpoint LPSS clocks')
Signed-off-by: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>
Acked-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Signed-off-by: Stephen Boyd <sboyd@codeaurora.org>