btrfs: consolidate fsverity_info lookup

btrfs: consolidate fsverity_info lookup

Look up the fsverity_info once in btrfs_do_readpage, and then use it
for all operations performed there, and do the same in end_folio_read
for all folios processed there.  The latter is also changed to derive
the inode from the btrfs_bio - while bbio->inode is optional, it is
always set for buffered reads.

This amortizes the lookup better once it becomes less efficient.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: David Sterba <dsterba@suse.com>
Link: https://lore.kernel.org/r/20260202060754.270269-11-hch@lst.de
Signed-off-by: Eric Biggers <ebiggers@kernel.org>