Adjust the passing value for GPU agent when do max single allocation test

For APU asics, the default configuration size of video memory is
relatively small, plus the reserved region, ratio of max alloc size to
the pool size may below the expected value, so adjust it.

Change-Id: I798b44d9532aa6a381a1cc19faa5a46110bf0ad6

rocrtst/suites/functional/memory_basic.cc

@@ -233,7 +233,7 @@ void MemoryTest::MaxSingleAllocationTest(hsa_agent_t ag,
   }
 
   if (ag_type == HSA_DEVICE_TYPE_GPU) {
-    EXPECT_GE((float)max_alloc_size/pool_sz, (float)15/16);
+    EXPECT_GE((float)max_alloc_size/pool_sz, (float)7/8);
   }
   if (verbosity() > 0) {
     std::cout << kSubTestSeparator << std::endl;