dm verity: fix DM_VERITY_OPTS_MAX value yet again

Must account for the possibility that "try_verify_in_tasklet" is used.

This is the same issue that was fixed with commit 160f99db -- it
is far too easy to miss that additional a new argument(s) require
bumping DM_VERITY_OPTS_MAX accordingly.

Fixes: 5721d4e5

 ("dm verity: Add optional "try_verify_in_tasklet" feature")
Signed-off-by: Mike Snitzer <snitzer@kernel.org>