media: gpu: vea_unittest: fix alignment on non ARM platforms

The base::AlignedAlloc expects a alignement multiple of sizeof(void*) :

DCHECK_EQ(alignment % sizeof(void*), 0U);

This fixes this error :

[0826/162544:FATAL:aligned_memory.cc(19)] Check failed: alignment % sizeof(void*) == 0U (1 vs. 0)

BUG=647570
TEST=run video_encode_accelerator_unittest on a non ARM platform

Review-Url: https://codereview.chromium.org/2281043002
Cr-Commit-Position: refs/heads/master@{#419124}

media/gpu/video_encode_accelerator_unittest.cc

@@ -165,7 +165,7 @@ int g_num_frames_to_encode = 0;
 // buffers.
 const size_t kPlatformBufferAlignment = 128;
 #else
-const size_t kPlatformBufferAlignment = 1;
+const size_t kPlatformBufferAlignment = 8;
 #endif
 
 inline static size_t AlignToPlatformRequirements(size_t value) {