Fix incorrect size in PNOR memory buffer clear routine

kestrel/src/kestrel.c

@@ -3835,7 +3835,7 @@ int kestrel_init(void)
     if (CLEAR_FLASH_CACHE_BUFFER_ON_STARTUP) {
         // Clear SPI Flash buffer
         KESTREL_LOG("Clearing host ROM internal buffer...");
-        memset32((uint32_t *)host_flash_buffer, 0xdeadbeef, (0x4000000 + 0x200000) / 4);
+        memset32((uint32_t *)host_flash_buffer, 0xdeadbeef, ((64 + 2) * 1024LL * 1024LL) / 4);
         KESTREL_LOG("\rInternal host ROM buffer cleared    ");
     }
     main_firmware_buffer.locked = 0;