squashfs: always use bio_kmalloc in squashfs_bio_read

If a plain kmalloc that is not backed by a mempool is safe here for a
large read (and the actual page allocations), it must also be for a
small one, so simplify the code a bit.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Acked-by: Phillip Lougher <phillip@squashfs.org.uk>
Reviewed-by: Chaitanya Kulkarni <kch@nvidia.com>
Link: https://lore.kernel.org/r/20220406061228.410163-3-hch@lst.de


Signed-off-by: Jens Axboe <axboe@kernel.dk>