i965/gen4: Subtract 1 from buffer sizes

i965/gen4: Subtract 1 from buffer sizes

The PRM states that the values put in Width, Height, and Depth should be
various bits from the value size - 1.  We seem to have done this wrong
more-or-less from the start.

Reviewed-by: Chad Versace <chad.versace@intel.com>
Cc: "11.1 11.2 12.0" <mesa-stable@lists.freedesktop.org>
(cherry picked from commit 2a1cc94d27c80929d91e38b4843333a5408d563e)