anv/allocator: Correctly set the number of buckets

anv/allocator: Correctly set the number of buckets

The range from ANV_MIN_STATE_SIZE_LOG2 to ANV_MAX_STATE_SIZE_LOG2 should
be inclusive and we have asserts that ensure that you never try to allocate
a state larger than (1 << ANV_MAX_STATE_SIZE_LOG2).  However, without
adding 1 to the difference, we allocate 1 too few bucckts and so, even
though we have an assert, anything landing in the last bucket will fail to
allocate properly..

Signed-off-by: Jason Ekstrand <jason@jlekstrand.net>
Cc: "12.0" <mesa-stable@lists.freedesktop.org>