[vdi] Fix -Wsign-compare warning. NFC.

- TeamCity build failed as `-Werror` is turned on.

Change-Id: Icd2cbd45f60e3c296894e8e73685e1d177f125a8

vdi/hip_platform.cpp

@@ -732,7 +732,7 @@ hipError_t ihipOccupancyMaxActiveBlocksPerMultiprocessor(
   }
 
   // Make sure the requested block size is smaller than max supported
-  if (blockSize > device.info().maxWorkGroupSize_) {
+  if (blockSize > int(device.info().maxWorkGroupSize_)) {
     numBlocks = 0;
     numGrids = 0;
     return hipSuccess;