vc4: Add missing braces in initializer

Silences the following GCC warning:

mesa/src/gallium/drivers/vc4/vc4_qir_schedule.c: In function 'qir_schedule_instructions':
mesa/src/gallium/drivers/vc4/vc4_qir_schedule.c:578:16: warning: missing braces around initializer [-Wmissing-braces]
         struct schedule_state state = { 0 };
                ^

Signed-off-by: Rhys Kidd <rhyskidd@gmail.com>
Signed-off-by: Eric Anholt <eric@anholt.net>

src/gallium/drivers/vc4/vc4_qir_schedule.c

@@ -575,7 +575,7 @@ void
 qir_schedule_instructions(struct vc4_compile *c)
 {
         void *mem_ctx = ralloc_context(NULL);
-        struct schedule_state state = { 0 };
+        struct schedule_state state = { { 0 } };
 
         if (debug) {
                 fprintf(stderr, "Pre-schedule instructions\n");