openrisc: sanitize use of orig_gpr11

The pt_regs struct had both a 'syscallno' field and an 'orig_gpr11' field
and it wasn't really clear how these were supposed to be used.  This patch
removes the syscallno field altogether and makes orig_gpr11 work more
like other architectures: keep track of syscall number in progress or
hold -1 for non-syscall exceptions.

Signed-off-by: Jonas Bonn <jonas@southpole.se>

arch/openrisc/kernel/signal.c

@@ -305,7 +305,7 @@ void do_signal(struct pt_regs *regs)
 	 * below mean that the syscall executed to completion and no
 	 * restart is necessary.
 	 */
-	if (regs->syscallno) {
+	if (regs->orig_gpr11) {
 		int restart = 0;
 
 		switch (regs->gpr[11]) {