Cast return value to int64_t for cache size (#28814)

Signed-off-by: tiehexue <tiehexue@hotmail.com>

csrc/cpu/cpu_attn_impl.hpp

@@ -754,7 +754,7 @@ class AttentionScheduler {
         return l2_cache_size >> 1;  // use 50% of L2 cache
       }
       // Fallback if sysctlbyname fails
-      return 128 * 1024 >> 1;  // use 50% of 128KB
+      return 128LL * 1024 >> 1;  // use 50% of 128KB
 #else
       long l2_cache_size = sysconf(_SC_LEVEL2_CACHE_SIZE);
       TORCH_CHECK_NE(l2_cache_size, -1);