freedreno/crashdec: Fix apparent off-by-one with ROQ size

freedreno/crashdec: Fix apparent off-by-one with ROQ size

I have multiple examples where this register is too large by one
when comparing to the ROQ read/write pointers in CP_ROQ_*_STAT and the
ROQ data itself, as if it includes the dword most recently read too. I
have an example where it's off by 2 compared to the read pointer, but
the read pointer is also off by 1 itself judging by the SQE program
counter, so that may just be them not getting synchronized. This
off-by-one was getting in the way of figuring out exactly IB2 was being
processed in the next commit.

Signed-off-by: Rob Clark <robdclark@chromium.org>
Part-of: <https://gitlab.freedesktop.org/mesa/mesa/-/merge_requests/19551>