usb: roles: fix include/linux/usb/role.h compile issue

when CONFIG_USB_ROLE_SWITCH is not defined,
add usb_role_switch_find_by_fwnode() definition which return NULL.

Fixes: c6919d5e0cd1 ("usb: roles: Add usb_role_switch_find_by_fwnode()")
Signed-off-by: Linyu Yuan <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Greg Kroah-Hartman <[e-mail]>

include/linux/usb/role.h

···
 static inline void usb_role_switch_put(struct usb_role_switch *sw) { }
 
 static inline struct usb_role_switch *
+usb_role_switch_find_by_fwnode(const struct fwnode_handle *fwnode)
+{
+	return NULL;
+}
+
+static inline struct usb_role_switch *
 usb_role_switch_register(struct device *parent,
 			 const struct usb_role_switch_desc *desc)
 {