i965: Fix off by one errors in texture buffer size calculations.

i965: Fix off by one errors in texture buffer size calculations.

The value that's split into width/height/depth needs to be the size of
the buffer minus one.  This makes it consistent with the constant buffer
and shader time SURFACE_STATE setup code.

Signed-off-by: Kenneth Graunke <kenneth@whitecape.org>
Reviewed-by: Eric Anholt <eric@anholt.net>