[rocBLAS] Refactor memory management in host_alloc.cpp

projects/rocblas/clients/common/host_alloc.cpp

@@ -54,10 +54,11 @@ void alloc_ptr_use(void* ptr, size_t size)
 void free_ptr_use(void* ptr, bool call_free)
 {
     std::lock_guard<std::mutex> lock(mem_mutex);
-    if(ptr && mem_allocated[ptr])
+    auto it = mem_allocated.find(ptr);
+    if(ptr && it != mem_allocated.end())
     {
-        mem_used -= mem_allocated[ptr];
-        mem_allocated.erase(ptr);
+        mem_used -= it->second;
+        mem_allocated.erase(it);
     }
     if(call_free)
         free(ptr);