Staging: batman-adv: return -EFAULT on copy_to_user errors

copy_to_user() returns the number of bites remaining but we want to
return a negative error code here.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: Sven Eckelmann <sven.eckelmann@gmx.de>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>

diff --git a/drivers/staging/batman-adv/device.c b/drivers/staging/batman-adv/device.c
index 7eb6559..32204b5 100644
--- a/drivers/staging/batman-adv/device.c
+++ b/drivers/staging/batman-adv/device.c
@@ -196,7 +196,7 @@
 	kfree(device_packet);
 
 	if (error)
-		return error;
+		return -EFAULT;
 
 	return sizeof(struct icmp_packet);
 }