[PATCH net-next] crush: fix using plain integer as NULL warning

Fixes the following sparse warning:
net/ceph/crush/mapper.c:517:76: warning: Using plain integer as NULL pointer
net/ceph/crush/mapper.c:728:68: warning: Using plain integer as NULL pointer

Signed-off-by: YueHaibing <redacted>
---
 net/ceph/crush/mapper.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/net/ceph/crush/mapper.c b/net/ceph/crush/mapper.c
index 417df67..3f323ed 100644
--- a/net/ceph/crush/mapper.c
+++ b/net/ceph/crush/mapper.c

@@ -514,7 +514,7 @@ static int crush_choose_firstn(const struct crush_map *map,
                                                in, work->work[-1-in->id],
                                                x, r,
                                                (choose_args ?
-                                                &choose_args[-1-in->id] : 0),
+                                                &choose_args[-1-in->id] : NULL),
                                                outpos);
                                if (item >= map->max_devices) {
                                        dprintk("   bad item %d\n", item);

@@ -725,7 +725,7 @@ static void crush_choose_indep(const struct crush_map *map,
                                        in, work->work[-1-in->id],
                                        x, r,
                                        (choose_args ?
-                                        &choose_args[-1-in->id] : 0),
+                                        &choose_args[-1-in->id] : NULL),
                                        outpos);
                                if (item >= map->max_devices) {
                                        dprintk("   bad item %d\n", item);