nios2: fix missing comment terminator from SPDX License commit

The commit 1a459660
  Add GPL-2.0+ SPDX-License-Identifier to source files

generated a warning due to a missing comment terminator.
  longlong.h:7:1: warning: "/*" within comment
Signed-off-by: NThomas Chou <thomas@wytron.com.tw>

arch/nios2/lib/longlong.h

@@ -3,6 +3,7 @@
    2005  Free Software Foundation, Inc.
 
  * SPDX-License-Identifier:	GPL-2.0+
+ */
 
 /* You have to define the following before including this file: