tests: fix warning ISO C90 forbids mixed declarations and code

Signed-off-by: Limin Wang <lance.lmwang@gmail.com>

tests/checkasm/vf_hflip.c

@@ -40,10 +40,10 @@ static void check_hflip(int step, const char * report_name){
     int i;
     int step_array[4] = {1, 1, 1, 1};
     FlipContext s;
-    s.bayer_plus1 = 1;
 
     declare_func(void, const uint8_t *src, uint8_t *dst, int w);
 
+    s.bayer_plus1 = 1;
     memset(src,     0, WIDTH_PADDED);
     memset(dst_ref, 0, WIDTH_PADDED);
     memset(dst_new, 0, WIDTH_PADDED);