btrfs: remove unused variable bio_offset from end_bbio_data_read()

The variable @bio_offset was introduced in commit 7ffd27e3 ("btrfs:
pass bio_offset to check_data_csum() directly"), when we are still using
the same endio function for both data and metadata.

Later we had several changes to data and metadata endio functions:

- Data verification is handled by btrfs bio layer

- Split data and metadata endio paths

Now for data path we no longer do any verification in
end_bbio_data_read(), as the verification is handled by btrfs bio layer
already.

Thus there is no need for such bio_offset variable.
Reviewed-by: Anand Jain <anand.jain@oracle.com>
Signed-off-by: Qu Wenruo <wqu@suse.com>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/extent_io.c

@@ -596,11 +596,6 @@ static void end_bbio_data_read(struct btrfs_bio *bbio)
 	struct bio *bio = &bbio->bio;
 	struct processed_extent processed = { 0 };
 	struct folio_iter fi;
-	/*
-	 * The offset to the beginning of a bio, since one bio can never be
-	 * larger than UINT_MAX, u32 here is enough.
-	 */
-	u32 bio_offset = 0;
 
 	ASSERT(!bio_flagged(bio, BIO_CLONED));
 	bio_for_each_folio_all(fi, &bbio->bio) {
@@ -667,10 +662,6 @@ static void end_bbio_data_read(struct btrfs_bio *bbio)
 		end_page_read(folio_page(folio, 0), uptodate, start, len);
 		endio_readpage_release_extent(&processed, BTRFS_I(inode),
 					      start, end, uptodate);
-
-		ASSERT(bio_offset + len > bio_offset);
-		bio_offset += len;
-
 	}
 	/* Release the last extent */
 	endio_readpage_release_extent(&processed, NULL, 0, 0, false);