ext4: unsigned int compared against zero

mainline inclusion
from mainline-5.2-rc1
commit fbbbbd2f28aec991f3fbc248df211550fbdfd58c
category: bugfix
bugzilla: 16402
CVE: NA
---------------------------

There are two cases where u32 variables n and err are being checked
for less than zero error values, the checks is always false because
the variables are not signed. Fix this by making the variables ints.

Addresses-Coverity: ("Unsigned compared against 0")
Fixes: 345c0dbf3a30 ("ext4: protect journal inode's blocks using block_validity")
Signed-off-by: NColin Ian King <colin.king@canonical.com>
Signed-off-by: NTheodore Ts'o <tytso@mit.edu>
Signed-off-by: Nyangerkun <yangerkun@huawei.com>
Reviewed-by: Nzhangyi (F) <yi.zhang@huawei.com>
Signed-off-by: NYang Yingliang <yangyingliang@huawei.com>

fs/ext4/block_validity.c

@@ -142,7 +142,8 @@ static int ext4_protect_reserved_inode(struct super_block *sb, u32 ino)
 	struct inode *inode;
 	struct ext4_sb_info *sbi = EXT4_SB(sb);
 	struct ext4_map_blocks map;
-	u32 i = 0, err = 0, num, n;
+	u32 i = 0, num;
+	int err = 0, n;
 
 	if ((ino < EXT4_ROOT_INO) ||
 	    (ino > le32_to_cpu(sbi->s_es->s_inodes_count)))