msm: pil: Make PIL shutdown ops optional

pil_shutdown() should be callable by pil drivers to de-assert proxy
votes, even if the pil driver doesn't implement shutdown ops.

Change-Id: I6a4468b07276d068765e13d41270d41f4bf5c570
Signed-off-by: Matt Wagantall <mattw@codeaurora.org>
diff --git a/arch/arm/mach-msm/peripheral-loader.c b/arch/arm/mach-msm/peripheral-loader.c
index affb451..fc9a0fa 100644
--- a/arch/arm/mach-msm/peripheral-loader.c
+++ b/arch/arm/mach-msm/peripheral-loader.c
@@ -656,7 +656,8 @@
 void pil_shutdown(struct pil_desc *desc)
 {
 	struct pil_priv *priv = desc->priv;
-	desc->ops->shutdown(desc);
+	if (desc->ops->shutdown)
+		desc->ops->shutdown(desc);
 	if (proxy_timeout_ms == 0 && desc->ops->proxy_unvote)
 		desc->ops->proxy_unvote(desc);
 	else