remoteproc: fix argument 2 of rproc_mem_entry_init

The rproc_mem_entry_init() call takes a pointer to a vm
as the second argument. The code is currently using a
plain 0 as "NULL". Change to using NULL to fix the
following sparse warnings:

drivers/remoteproc/remoteproc_core.c:339:49: warning: Using plain integer as NULL pointer
drivers/remoteproc/remoteproc_core.c:916:46: warning: Using plain integer as NULL pointer
Signed-off-by: Ben Dooks <ben.dooks@codethink.co.uk>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>

drivers/remoteproc/remoteproc_core.c

@@ -334,7 +334,8 @@ int rproc_alloc_vring(struct rproc_vdev *rvdev, int i)
 			return -ENOMEM;
 	} else {
 		/* Register carveout in in list */
-		mem = rproc_mem_entry_init(dev, 0, 0, size, rsc->vring[i].da,
+		mem = rproc_mem_entry_init(dev, NULL, 0,
+					   size, rsc->vring[i].da,
 					   rproc_alloc_carveout,
 					   rproc_release_carveout,
 					   "vdev%dvring%d",
@@ -911,7 +912,7 @@ static int rproc_handle_carveout(struct rproc *rproc,
 	}
 
 	/* Register carveout in in list */
-	carveout = rproc_mem_entry_init(dev, 0, 0, rsc->len, rsc->da,
+	carveout = rproc_mem_entry_init(dev, NULL, 0, rsc->len, rsc->da,
 					rproc_alloc_carveout,
 					rproc_release_carveout, rsc->name);
 	if (!carveout) {