Fix warnings from static analaysis tools

Change-Id: Iad227b07b6c3f5beebef971cabec787b01e6f51f

av1/common/av1_txfm.h

@@ -67,6 +67,7 @@ static const int32_t cospi_arr[7][64] = {
 };
 
 static INLINE int32_t round_shift(int32_t value, int bit) {
+  assert(bit >= 1);
   return (value + (1 << (bit - 1))) >> bit;
 }
 

av1/encoder/encoder.c

@@ -2821,6 +2821,7 @@ static void scale_and_extend_frame(const YV12_BUFFER_CONFIG *src,
   const int taps = interp_filter_params.taps;
   int x, y, i;
 
+  assert(planes <= 3);
   for (y = 0; y < dst_h; y += 16) {
     for (x = 0; x < dst_w; x += 16) {
       for (i = 0; i < planes; ++i) {

test/av1_convolve_test.cc

@@ -103,9 +103,10 @@ TEST(AV1ConvolveTest, av1_convolve) {
   int subpel_x_q4;
   int subpel_y_q4;
 
+  ASSERT_LE(filter_size, 12);
   setup_convolve();
 
-  for (int i = 0; i < filter_size * filter_size; i++) {
+  for (int i = 0; i < static_cast<int>(sizeof(src) / sizeof(src[0])); i++) {
     src[i] = rnd.Rand16() % (1 << 8);
   }