usb: gadget: f_acm: Fix configfs attr name

Correct attribute name is port_num not num.

Fixes: ea6bd6b1 ("usb-gadget/f_acm: use per-attribute show and store methods")
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Krzysztof Opasiak <k.opasiak@samsung.com>
Signed-off-by: Felipe Balbi <balbi@kernel.org>

drivers/usb/gadget/function/f_acm.c

@@ -777,10 +777,10 @@ static ssize_t f_acm_port_num_show(struct config_item *item, char *page)
 	return sprintf(page, "%u\n", to_f_serial_opts(item)->port_num);
 }
 
-CONFIGFS_ATTR_RO(f_acm_port_, num);
+CONFIGFS_ATTR_RO(f_acm_, port_num);
 
 static struct configfs_attribute *acm_attrs[] = {
-	&f_acm_port_attr_num,
+	&f_acm_attr_port_num,
 	NULL,
 };