usb: gadget: add '__ref' for rndis_config_register() and cdc_config_register()

They are only called by '__ref' function multi_bind(), and they will
call '__init' functions, so recommend to let them '__ref' too.

The related warnings:

  WARNING: drivers/usb/gadget/g_multi.o(.text+0xded6): Section mismatch in reference from the variable .LM2921 to the variable .init.text:_rndis_do_config
  The function .LM2921() references
  the variable __init _rndis_do_config.
  This is often because .LM2921 lacks a __init
  annotation or the annotation of _rndis_do_config is wrong.

  WARNING: drivers/usb/gadget/g_multi.o(.text+0xdf16): Section mismatch in reference from the variable .LM2953 to the variable .init.text:_cdc_do_config
  The function .LM2953() references
  the variable __init _cdc_do_config.
  This is often because .LM2953 lacks a __init
  annotation or the annotation of _cdc_do_config is wrong.
Signed-off-by: Chen Gang <gang.chen@asianux.com>
Signed-off-by: Felipe Balbi <balbi@ti.com>

drivers/usb/gadget/multi.c

@@ -179,7 +179,7 @@ static __init int rndis_do_config(struct usb_configuration *c)
 	return ret;
 }
 
-static int rndis_config_register(struct usb_composite_dev *cdev)
+static __ref int rndis_config_register(struct usb_composite_dev *cdev)
 {
 	static struct usb_configuration config = {
 		.bConfigurationValue	= MULTI_RNDIS_CONFIG_NUM,
@@ -194,7 +194,7 @@ static int rndis_config_register(struct usb_composite_dev *cdev)
 
 #else
 
-static int rndis_config_register(struct usb_composite_dev *cdev)
+static __ref int rndis_config_register(struct usb_composite_dev *cdev)
 {
 	return 0;
 }
@@ -241,7 +241,7 @@ static __init int cdc_do_config(struct usb_configuration *c)
 	return ret;
 }
 
-static int cdc_config_register(struct usb_composite_dev *cdev)
+static __ref int cdc_config_register(struct usb_composite_dev *cdev)
 {
 	static struct usb_configuration config = {
 		.bConfigurationValue	= MULTI_CDC_CONFIG_NUM,
@@ -256,7 +256,7 @@ static int cdc_config_register(struct usb_composite_dev *cdev)
 
 #else
 
-static int cdc_config_register(struct usb_composite_dev *cdev)
+static __ref int cdc_config_register(struct usb_composite_dev *cdev)
 {
 	return 0;
 }