mfd: omap-usb: Depend on COMMON_CLK to fix compile tests

The MFD_OMAP_USB_HOST uses Common Clock Framework thus it cannot be
built on platforms without it (e.g. compile test on MIPS with LANTIQ):

    mips-linux-ld: drivers/mfd/omap-usb-host.o: in function `usbhs_omap_probe':
    omap-usb-host.c:(.text+0x940): undefined reference to `clk_set_parent'
Reported-by: kernel test robot <lkp@intel.com>
Signed-off-by: Krzysztof Kozlowski <krzk@kernel.org>
Signed-off-by: Lee Jones <lee.jones@linaro.org>

drivers/mfd/Kconfig

@@ -1443,6 +1443,7 @@ config MFD_TI_LMU
 config MFD_OMAP_USB_HOST
 	bool "TI OMAP USBHS core and TLL driver"
 	depends on USB_EHCI_HCD_OMAP || USB_OHCI_HCD_OMAP3
+	depends on COMMON_CLK
 	default y
 	help
 	  This is the core driver for the OAMP EHCI and OHCI drivers.