MLK-12421 usb: chipidea: fix build warning if disable CONFIG_USB_CHIPIDEA_HOST

MLK-12421 usb: chipidea: fix build warning if disable CONFIG_USB_CHIPIDEA_HOST

Fix chipidea usb driver compile warning if CONFIG_USB_CHIPIDEA_HOST
is disabled:
In file included from drivers/usb/chipidea/otg.c:26:0:
drivers/usb/chipidea/host.h:23:13: warning: 'ci_hdrc_host_driver_init'
defined but not used [-Wunused-function]
 static void ci_hdrc_host_driver_init(void)
             ^
  CC      drivers/usb/chipidea/otg_fsm.o
In file included from drivers/usb/chipidea/otg_fsm.c:34:0:
drivers/usb/chipidea/host.h:23:13: warning: 'ci_hdrc_host_driver_init'
defined but not used [-Wunused-function]
 static void ci_hdrc_host_driver_init(void)
             ^

Signed-off-by: Li Jun <jun.li@nxp.com>