[Flang][liboffload] Set default for LIBOMPTARGET_SHARED_DESCRIPTOR_MAX_SIZE to 0 (bytes) (llvm#3042)

Author: ronlieb

offload/plugins-nextgen/amdgpu/src/rtl.cpp

@@ -3023,7 +3023,7 @@ struct AMDGPUDeviceTy : public GenericDeviceTy, AMDGenericDeviceTy {
                                     1 * 1024 * 1024), // 1MB
         OMPX_DGPUMaps("OMPX_DGPU_MAPS", false),
         OMPX_SharedDescriptorMaxSize("LIBOMPTARGET_SHARED_DESCRIPTOR_MAX_SIZE",
-                                     96),
+                                     0),
         OMPX_EnableDevice2DeviceMemAccess(
             "OMPX_ENABLE_DEVICE_TO_DEVICE_MEM_ACCESS", false),
         AMDGPUStreamManager(*this, Agent), AMDGPUEventManager(*this),