f2fs: fix to show discard_unit mount opt

Convert to show discard_unit only when has DISCARD opt.
Signed-off-by: Yangtao Li <frank.li@vivo.com>
Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org>

fs/f2fs/super.c

@@ -1908,10 +1908,17 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 		seq_puts(seq, ",disable_roll_forward");
 	if (test_opt(sbi, NORECOVERY))
 		seq_puts(seq, ",norecovery");
-	if (test_opt(sbi, DISCARD))
+	if (test_opt(sbi, DISCARD)) {
 		seq_puts(seq, ",discard");
-	else
+		if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_BLOCK)
+			seq_printf(seq, ",discard_unit=%s", "block");
+		else if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SEGMENT)
+			seq_printf(seq, ",discard_unit=%s", "segment");
+		else if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SECTION)
+			seq_printf(seq, ",discard_unit=%s", "section");
+	} else {
 		seq_puts(seq, ",nodiscard");
+	}
 	if (test_opt(sbi, NOHEAP))
 		seq_puts(seq, ",no_heap");
 	else
@@ -2035,13 +2042,6 @@ static int f2fs_show_options(struct seq_file *seq, struct dentry *root)
 	if (test_opt(sbi, ATGC))
 		seq_puts(seq, ",atgc");
 
-	if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_BLOCK)
-		seq_printf(seq, ",discard_unit=%s", "block");
-	else if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SEGMENT)
-		seq_printf(seq, ",discard_unit=%s", "segment");
-	else if (F2FS_OPTION(sbi).discard_unit == DISCARD_UNIT_SECTION)
-		seq_printf(seq, ",discard_unit=%s", "section");
-
 	if (F2FS_OPTION(sbi).memory_mode == MEMORY_MODE_NORMAL)
 		seq_printf(seq, ",memory=%s", "normal");
 	else if (F2FS_OPTION(sbi).memory_mode == MEMORY_MODE_LOW)