usb: cdc-wdm: fix build error when CONFIG_WWAN_CORE is not set

Gcc report build error as following when CONFIG_WWAN_CORE is not set:

x86_64-linux-gnu-ld: drivers/usb/class/cdc-wdm.o: in function `wdm_disconnect':
cdc-wdm.c:(.text+0xb2a): undefined reference to `wwan_remove_port'
x86_64-linux-gnu-ld: drivers/usb/class/cdc-wdm.o: in function `wdm_in_callback':
cdc-wdm.c:(.text+0xf23): undefined reference to `wwan_port_rx'
x86_64-linux-gnu-ld: drivers/usb/class/cdc-wdm.o: in function `wdm_wwan_port_stop':
cdc-wdm.c:(.text+0x127d): undefined reference to `wwan_port_get_drvdata'
x86_64-linux-gnu-ld: drivers/usb/class/cdc-wdm.o: in function `wdm_wwan_port_tx':
cdc-wdm.c:(.text+0x12d9): undefined reference to `wwan_port_get_drvdata'
x86_64-linux-gnu-ld: cdc-wdm.c:(.text+0x13c1): undefined reference to `wwan_port_txoff'
x86_64-linux-gnu-ld: drivers/usb/class/cdc-wdm.o: in function `wdm_wwan_port_start':
cdc-wdm.c:(.text+0x13e0): undefined reference to `wwan_port_get_drvdata'
x86_64-linux-gnu-ld: cdc-wdm.c:(.text+0x1431): undefined reference to `wwan_port_txon'
x86_64-linux-gnu-ld: drivers/usb/class/cdc-wdm.o: in function `wdm_wwan_port_tx_complete':
cdc-wdm.c:(.text+0x14a4): undefined reference to `wwan_port_txon'
x86_64-linux-gnu-ld: drivers/usb/class/cdc-wdm.o: in function `wdm_create.cold':
cdc-wdm.c:(.text.unlikely+0x209): undefined reference to `wwan_create_port'

Using CONFIG_WWAN_CORE instead of CONFIG_WWAN to avoid build error.

Fixes: cac6fb01 ("usb: class: cdc-wdm: WWAN framework integration")
Reported-by: Hulk Robot <hulkci@huawei.com>
Reviewed-by: Loic Poulain <loic.poulain@linaro.org>
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Link: https://lore.kernel.org/r/20210521021010.2490930-1-weiyongjun1@huawei.comSigned-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/class/cdc-wdm.c

@@ -824,7 +824,7 @@ static struct usb_class_driver wdm_class = {
 };
 
 /* --- WWAN framework integration --- */
-#ifdef CONFIG_WWAN
+#ifdef CONFIG_WWAN_CORE
 static int wdm_wwan_port_start(struct wwan_port *port)
 {
 	struct wdm_device *desc = wwan_port_get_drvdata(port);
@@ -963,11 +963,11 @@ static void wdm_wwan_rx(struct wdm_device *desc, int length)
 	/* inbuf has been copied, it is safe to check for outstanding data */
 	schedule_work(&desc->service_outs_intr);
 }
-#else /* CONFIG_WWAN */
+#else /* CONFIG_WWAN_CORE */
 static void wdm_wwan_init(struct wdm_device *desc) {}
 static void wdm_wwan_deinit(struct wdm_device *desc) {}
 static void wdm_wwan_rx(struct wdm_device *desc, int length) {}
-#endif /* CONFIG_WWAN */
+#endif /* CONFIG_WWAN_CORE */
 
 /* --- error handling --- */
 static void wdm_rxwork(struct work_struct *work)