qnx4: handle set_blocksize failures

qnx4: handle set_blocksize failures

qnx4 uses buffer_heads, which don't handle block size > PAGE_SIZE well.
Without this, mounting will hit the

        BUG_ON(offset >= folio_size(folio));

in folio_set_bh on the first __bread_gfp call.

Signed-off-by: Christoph Hellwig <hch@lst.de>
Link: https://patch.msgid.link/20260511071701.2456211-4-hch@lst.de
Acked-by: Anders Larsen <al@alarsen.net>
Signed-off-by: Christian Brauner (Amutable) <brauner@kernel.org>