```Amend cdef_copy_rect test suites

Those functions are called only for values of width that are either 4 or
a multiple of 8, so reflect that in the tests.

Change-Id: Ida83d3d6301228010eac611ed92686d5f154b350
```
```diff --git a/test/cdef_test.cc b/test/cdef_test.cc
--- a/test/cdef_test.cc
+++ b/test/cdef_test.cc
```
```@@ -441,9 +441,10 @@
constexpr int stride = MAX_CDEF_BLOCK;
int error = 0;
for (int k = 0; k < kIterations && !error; k++) {
-      // Generate a random value between 1 and 256, making sure height is even.
-      // Test once for very small values to avoid potential overflows.
-      const int width = k == 0 ? 4 : rnd_.Rand8() % 256 + 1;
+      // This function operates on values of width that are either 4 or a
+      // multiple of 8. For height, generate a random value between 1 and 256,
+      // making sure it is even.
+      const int width = k == 0 ? 4 : (rnd_.Rand8() % 32 + 1) * 8;
const int height = k == 0 ? 4 : (rnd_.Rand8() % 128 + 1) * 2;
for (int i = 0; i < height; i++) {
for (int j = 0; j < width; j++) {
@@ -524,9 +525,10 @@
constexpr int stride = MAX_CDEF_BLOCK;
int error = 0;
for (int k = 0; k < kIterations && !error; k++) {
-      // Generate a random value between 1 and 256, making sure height is even.
-      // Test once for very small values to avoid potential overflows.
-      const int width = k == 0 ? 4 : rnd_.Rand8() % 256 + 1;
+      // This function operates on values of width that are either 4 or a
+      // multiple of 8. For height, generate a random value between 1 and 256,
+      // making sure it is even.
+      const int width = k == 0 ? 4 : (rnd_.Rand8() % 32 + 1) * 8;
const int height = k == 0 ? 4 : (rnd_.Rand8() % 128 + 1) * 2;
for (int i = 0; i < height; i++) {
for (int j = 0; j < width; j++) {
```