squashfs: don't include buffer_head.h

Squashfs has stopped using buffers heads in 93e72b3c
("squashfs: migrate from ll_rw_block usage to BIO").

Link: https://lkml.kernel.org/r/20230517071622.245151-1-hch@lst.de


Signed-off-by: Christoph Hellwig <hch@lst.de>
Reviewed-by: Pankaj Raghav <p.raghav@samsung.com>
Reviewed-by: Phillip Lougher <phillip@squashfs.org.uk>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>