xen/netback: fix build warning

mainline inclusion
from mainline-v6.1
commit 7dfa764e
category: bugfix
bugzilla: 188138
CVE: CVE-2022-3643

Reference: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=7dfa764e0223a324366a2a1fc056d4d9d4e95491

--------------------------------

Commit ad7f402a ("xen/netback: Ensure protocol headers don't fall in
the non-linear area") introduced a (valid) build warning. There have
even been reports of this problem breaking networking of Xen guests.

Fixes: ad7f402a ("xen/netback: Ensure protocol headers don't fall in the non-linear area")
Signed-off-by: NJuergen Gross <jgross@suse.com>
Reviewed-by: NJan Beulich <jbeulich@suse.com>
Reviewed-by: NRoss Lagerwall <ross.lagerwall@citrix.com>
Tested-by: NJason Andryuk <jandryuk@gmail.com>
Signed-off-by: NJuergen Gross <jgross@suse.com>
Signed-off-by: NZhengchao Shao <shaozhengchao@huawei.com>
Reviewed-by: NYue Haibing <yuehaibing@huawei.com>
Reviewed-by: NXiu Jianfeng <xiujianfeng@huawei.com>
Signed-off-by: NZheng Zengkai <zhengzengkai@huawei.com>

drivers/net/xen-netback/netback.c

@@ -528,7 +528,7 @@ static int xenvif_tx_check_gop(struct xenvif_queue *queue,
 	const bool sharedslot = nr_frags &&
 				frag_get_pending_idx(&shinfo->frags[0]) ==
 				    copy_pending_idx(skb, copy_count(skb) - 1);
-	int i, err;
+	int i, err = 0;
 
 	for (i = 0; i < copy_count(skb); i++) {
 		int newerr;