st/nine: Fix incompatible-pointer-types-discards-qualifiers errors.

../src/gallium/state_trackers/nine/nine_ff.c:129:28: error: initializing 'struct nine_ff_vs_key *' with an expression of type 'const void *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers] struct nine_ff_vs_key *vs = key; ^ ~~~ ../src/gallium/state_trackers/nine/nine_ff.c:145:28: error: initializing 'struct nine_ff_ps_key *' with an expression of type 'const void *' discards qualifiers [-Werror,-Wincompatible-pointer-types-discards-qualifiers] struct nine_ff_ps_key *ps = key; ^ ~~~

Fixes: fdd96578 ("nine: Add state tracker nine for Direct3D9 (v3)") Signed-off-by: Vinson Lee vlee@freedesktop.org