i965: Switch fs_inst to the non-zeroing allocator.

i965: Switch fs_inst to the non-zeroing allocator.

All member variables of fs_inst are already being initialized from its
constructor, it's not necessary to use rzalloc to allocate its memory,
and doing so makes it more likely that we will start relying on the
allocator to zero out all memory if the class is ever extended with
new member variables.

That's bad because it ties objects to some specific allocation scheme,
and gives unpredictable results when an object is created with a
different allocator -- Stack allocation, array allocation, or
aggregation inside a different object are some of the useful
possibilities that come to my mind.

Reviewed-by: Kenneth Graunke <kenneth@whitecape.org>