btrfs: Kill some bi_idx references

For immutable bio vecs, I've been auditing and removing bi_idx
references. These were harmless, but removing them will make auditing
easier.

scrub_bio_end_io_worker() was open coding a bio_reset() - but this
doesn't appear to have been needed for anything as right after it does a
bio_put(), and perusing the code it doesn't appear anything else was
holding a reference to the bio.

The other use end_bio_extent_readpage() was just for a pr_debug() -
changed it to something that might be a bit more useful.

Signed-off-by: Kent Overstreet <koverstreet@google.com>
CC: Chris Mason <chris.mason@oracle.com>
CC: Stefan Behrens <sbehrens@giantdisaster.de>
diff --git a/fs/btrfs/extent_io.c b/fs/btrfs/extent_io.c
index 3ad84f5..90bd9f7 100644
--- a/fs/btrfs/extent_io.c
+++ b/fs/btrfs/extent_io.c
@@ -2306,8 +2306,8 @@
 		struct extent_state *cached = NULL;
 		struct extent_state *state;
 
-		pr_debug("end_bio_extent_readpage: bi_vcnt=%d, idx=%d, err=%d, "
-			 "mirror=%ld\n", bio->bi_vcnt, bio->bi_idx, err,
+		pr_debug("end_bio_extent_readpage: bi_sector=%llu, err=%d, "
+			 "mirror=%ld\n", (u64)bio->bi_sector, err,
 			 (long int)bio->bi_bdev);
 		tree = &BTRFS_I(page->mapping->host)->io_tree;