phy: rockchip-inno-usb2: add COMMON_CLK dependency

On kernel builds without COMMON_CLK, the newly added rockchip-inno-usb2
driver fails to build:

drivers/phy/phy-rockchip-inno-usb2.c:124:16: error: field 'clk480m_hw'
has incomplete type
   struct clk_hw clk480m_hw;

In file included from include/linux/clk.h:16:0
                 from drivers/phy/phy-rockchip-inno-usb2.c:17:
include/linux/kernel.h:831:48: error: initialization from incompatible
pointer type [-Werror=incompatible-pointer-types]
   const typeof( ((type *)0)->member ) *__mptr = (ptr); \

  ... ...

Signed-off-by: Frank Wang <frank.wang@rock-chips.com>
Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Heiko Stuebner <heiko@sntech.de>