x86: signal_64.c: arg for restore_i387_xstate() is void __user *

restore_i387_xstate() is declared as:

  int restore_i387_xstate(void __user *buf);

so, make the variable buf void __user *.
Signed-off-by: NHiroshi Shimamoto <h-shimamoto@ct.jp.nec.com>
Signed-off-by: NIngo Molnar <mingo@elte.hu>

arch/x86/kernel/signal_64.c

@@ -94,7 +94,8 @@ restore_sigcontext(struct pt_regs *regs, struct sigcontext __user *sc,
 	}
 
 	{
-		struct _fpstate __user *buf;
+		void __user *buf;
+
 		err |= __get_user(buf, &sc->fpstate);
 		err |= restore_i387_xstate(buf);
 	}