ext4: fix unused-but-set-variable warning in ext4_add_entry()

Warning is found when compile with "-Wunused-but-set-variable":

fs/ext4/namei.c: In function ‘ext4_add_entry’:
fs/ext4/namei.c:2167:23: warning: variable ‘sbi’ set but not used
[-Wunused-but-set-variable]
  struct ext4_sb_info *sbi;
                       ^~~
Fix this by moving the variable @sbi under CONFIG_UNICODE.
Signed-off-by: Yunfeng Ye <yeyunfeng@huawei.com>
Reviewed-by: Ritesh Harjani <riteshh@linux.ibm.com>
Link: https://lore.kernel.org/r/cb5eb904-224a-9701-c38f-cb23514b1fff@huawei.comSigned-off-by: Theodore Ts'o <tytso@mit.edu>

fs/ext4/namei.c

@@ -2164,7 +2164,9 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
 	struct buffer_head *bh = NULL;
 	struct ext4_dir_entry_2 *de;
 	struct super_block *sb;
+#ifdef CONFIG_UNICODE
 	struct ext4_sb_info *sbi;
+#endif
 	struct ext4_filename fname;
 	int	retval;
 	int	dx_fallback=0;
@@ -2176,12 +2178,12 @@ static int ext4_add_entry(handle_t *handle, struct dentry *dentry,
 		csum_size = sizeof(struct ext4_dir_entry_tail);
 
 	sb = dir->i_sb;
-	sbi = EXT4_SB(sb);
 	blocksize = sb->s_blocksize;
 	if (!dentry->d_name.len)
 		return -EINVAL;
 
 #ifdef CONFIG_UNICODE
+	sbi = EXT4_SB(sb);
 	if (ext4_has_strict_mode(sbi) && IS_CASEFOLDED(dir) &&
 	    sbi->s_encoding && utf8_validate(sbi->s_encoding, &dentry->d_name))
 		return -EINVAL;