usb: chipidea: add inline for ci_hdrc_host_driver_init if host is not defined

Otherwise, there is a build warning if this header file is included
by non host source file, eg, otg.c.

Signed-off-by: Jun Li <jun.li@nxp.com>
Signed-off-by: Peter Chen <peter.chen@nxp.com>
Link: https://lore.kernel.org/r/20200122014639.22667-3-peter.chen@nxp.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>