usb-gadget/f_acm: use per-attribute show and store methods

To simplify the configfs interface and remove boilerplate code that also
causes binary bloat.

Signed-off-by: Christoph Hellwig <[e-mail]>
Reviewed-by: Andrzej Pietrasiewicz <[e-mail]>
Acked-by: Felipe Balbi <[e-mail]>
Signed-off-by: Nicholas Bellinger <[e-mail]>

drivers/usb/gadget/function/f_acm.c

···
 			func_inst.group);
 }
 
-CONFIGFS_ATTR_STRUCT(f_serial_opts);
-static ssize_t f_acm_attr_show(struct config_item *item,
-				 struct configfs_attribute *attr,
-				 char *page)
-{
-	struct f_serial_opts *opts = to_f_serial_opts(item);
-	struct f_serial_opts_attribute *f_serial_opts_attr =
-		container_of(attr, struct f_serial_opts_attribute, attr);
-	ssize_t ret = 0;
-
-	if (f_serial_opts_attr->show)
-		ret = f_serial_opts_attr->show(opts, page);
-	return ret;
-}
-
 static void acm_attr_release(struct config_item *item)
 {
 	struct f_serial_opts *opts = to_f_serial_opts(item);
···
 
 static struct configfs_item_operations acm_item_ops = {
 	.release                = acm_attr_release,
-	.show_attribute		= f_acm_attr_show,
 };
 
-static ssize_t f_acm_port_num_show(struct f_serial_opts *opts, char *page)
+static ssize_t f_acm_port_num_show(struct config_item *item, char *page)
 {
-	return sprintf(page, "%u\n", opts->port_num);
+	return sprintf(page, "%u\n", to_f_serial_opts(item)->port_num);
 }
 
-static struct f_serial_opts_attribute f_acm_port_num =
-	__CONFIGFS_ATTR_RO(port_num, f_acm_port_num_show);
-
+CONFIGFS_ATTR_RO(f_acm_port_, num);
 
 static struct configfs_attribute *acm_attrs[] = {
-	&f_acm_port_num.attr,
+	&f_acm_port_attr_num,
 	NULL,
 };