um: Fix return value in ubd_init()

When kmalloc_array() fails to allocate memory, the ubd_init()
should return -ENOMEM instead of -1. So, fix it.

Fixes: f88f0bdf ("um: UBD Improvements")
Signed-off-by: Duoming Zhou <duoming@zju.edu.cn>
Reviewed-by: Johannes Berg <johannes@sipsolutions.net>
Signed-off-by: Richard Weinberger <richard@nod.at>

arch/um/drivers/ubd_kern.c

@@ -1092,7 +1092,7 @@ static int __init ubd_init(void)
 
 	if (irq_req_buffer == NULL) {
 		printk(KERN_ERR "Failed to initialize ubd buffering\n");
-		return -1;
+		return -ENOMEM;
 	}
 	io_req_buffer = kmalloc_array(UBD_REQ_BUFFER_SIZE,
 				      sizeof(struct io_thread_req *),
@@ -1103,7 +1103,7 @@ static int __init ubd_init(void)
 
 	if (io_req_buffer == NULL) {
 		printk(KERN_ERR "Failed to initialize ubd buffering\n");
-		return -1;
+		return -ENOMEM;
 	}
 	platform_driver_register(&ubd_driver);
 	mutex_lock(&ubd_lock);