bcachefs: fix the display format for show-super

There are three keys displayed in non-uniform format.
Let's fix them.

[Before]
```
Label:	testbcachefs
Version:	1.9: (unknown version)
Version upgrade complete:	0.0: (unknown version)
```

[After]
```
Label:					testbcachefs
Version:				1.9: (unknown version)
Version upgrade complete:		0.0: (unknown version)
```

Fixes: 7423330e ("bcachefs: prt_printf() now respects \r\n\t")
Signed-off-by: Hongbo Li <lihongbo22@huawei.com>
Signed-off-by: Kent Overstreet <kent.overstreet@linux.dev>

fs/bcachefs/super-io.c

@@ -1310,15 +1310,15 @@ void bch2_sb_to_text(struct printbuf *out, struct bch_sb *sb,
 
 	prt_printf(out, "Device index:\t%u\n", sb->dev_idx);
 
-	prt_str(out, "Label:\t");
+	prt_printf(out, "Label:\t");
 	prt_printf(out, "%.*s", (int) sizeof(sb->label), sb->label);
 	prt_newline(out);
 
-	prt_str(out, "Version:\t");
+	prt_printf(out, "Version:\t");
 	bch2_version_to_text(out, le16_to_cpu(sb->version));
 	prt_newline(out);
 
-	prt_str(out, "Version upgrade complete:\t");
+	prt_printf(out, "Version upgrade complete:\t");
 	bch2_version_to_text(out, BCH_SB_VERSION_UPGRADE_COMPLETE(sb));
 	prt_newline(out);