i965/vs: Fix NULL pointer dereference in pre-Gen6 push constant loading.

i965/vs: Fix NULL pointer dereference in pre-Gen6 push constant loading.

According to the comment, we need to load /some/ push constants on
pre-Gen6 hardware or the GPU will hang.  The existing code set these
bogus parameters to NULL pointers; unfortunately, the code in
brw_curbe.c that loads them dereferences those pointers.  So, change
them to be pointers to an actual floating point value of 0.0.

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