btrfs: use bvec_phys() in compressed_bio_last_folio()

This is open-coded bvec_phys(), also remove direct use of bv_page.

Reviewed-by: Qu Wenruo <wqu@suse.com>
Reviewed-by: Boris Burkov <boris@bur.io>
Tested-by: Boris Burkov <boris@bur.io>
Signed-off-by: Matthew Wilcox (Oracle) <willy@infradead.org>
Signed-off-by: David Sterba <dsterba@suse.com>

fs/btrfs/inode.c

@@ -820,7 +820,7 @@ static struct folio *compressed_bio_last_folio(struct compressed_bio *cb)
 	ASSERT(bio->bi_vcnt);
 
 	bvec = &bio->bi_io_vec[bio->bi_vcnt - 1];
-	paddr = page_to_phys(bvec->bv_page) + bvec->bv_offset + bvec->bv_len - 1;
+	paddr = bvec_phys(bvec) + bvec->bv_len - 1;
 	return page_folio(phys_to_page(paddr));
 }