powerpc/iseries: Mark signal_vsp_instruction() as maybe unused

signal_vsp_instruction() is currently only used if CONFIG_PROC_FS
is enabled. However logically it has nothing to do with PROC_FS,
so rather than making it depend on that mark it as maybe unused.
Signed-off-by: Michael Ellerman <michael@ellerman.id.au>
Signed-off-by: Benjamin Herrenschmidt <benh@kernel.crashing.org>

arch/powerpc/platforms/iseries/mf.c

@@ -267,7 +267,8 @@ static struct pending_event *new_pending_event(void)
 	return ev;
 }
 
-static int signal_vsp_instruction(struct vsp_cmd_data *vsp_cmd)
+static int __maybe_unused
+signal_vsp_instruction(struct vsp_cmd_data *vsp_cmd)
 {
 	struct pending_event *ev = new_pending_event();
 	int rc;