btrfs: fix uninitialized variable warning in get_inode_gen

Anybody that calls get_inode_gen() can have an uninitialized gen if
there's an error.  This isn't a big deal because all the users just exit
if they get an error, however it makes -Wmaybe-uninitialized complain,
so fix this up to always initialize the passed in gen, this quiets all
of the uninitialized warnings in send.c.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: Josef Bacik <josef@toxicpanda.com>
Reviewed-by: David Sterba <dsterba@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/send.c

@@ -956,14 +956,12 @@ static int get_inode_info(struct btrfs_root *root, u64 ino,
 static int get_inode_gen(struct btrfs_root *root, u64 ino, u64 *gen)
 {
 	int ret;
-	struct btrfs_inode_info info;
+	struct btrfs_inode_info info = { 0 };
 
-	if (!gen)
-		return -EPERM;
+	ASSERT(gen);
 
 	ret = get_inode_info(root, ino, &info);
-	if (!ret)
-		*gen = info.gen;
+	*gen = info.gen;
 	return ret;
 }