md-cluster: fix rmmod issue when md_cluster convert bitmap to none

update_array_info misses calling module_put when removing cluster bitmap.

steps to reproduce:
```
node1 # mdadm -C /dev/md0 -b clustered -e 1.2 -n 2 -l mirror /dev/sda
/dev/sdb
mdadm: array /dev/md0 started.
node1 # lsmod | egrep "dlm|md_|raid1"
md_cluster             28672  1
dlm                   212992  14 md_cluster
configfs               57344  2 dlm
raid1                  53248  1
md_mod                176128  2 raid1,md_cluster
node1 # mdadm -G /dev/md0 -b none
node1 # lsmod | egrep "dlm|md_|raid1"
md_cluster             28672  1 <== should be zero
dlm                   212992  9 md_cluster
configfs               57344  2 dlm
raid1                  53248  1
md_mod                176128  2 raid1,md_cluster
node1 # mdadm -G /dev/md0 -b clustered
node1 # lsmod | egrep "dlm|md_|raid1"
md_cluster             28672  2 <== increase
dlm                   212992  14 md_cluster
configfs               57344  2 dlm
raid1                  53248  1
md_mod                176128  2 raid1,md_cluster
node1 # mdadm -G /dev/md0 -b none
node1 # mdadm -G /dev/md0 -b clustered
node1 # lsmod | egrep "dlm|md_|raid1"
md_cluster             28672  3 <== increase
dlm                   212992  14 md_cluster
configfs               57344  2 dlm
raid1                  53248  1
md_mod                176128  2 raid1,md_cluster
```
Reviewed-by: NeilBrown <neilb@suse.de>
Signed-off-by: Zhao Heming <heming.zhao@suse.com>
Signed-off-by: Song Liu <songliubraving@fb.com>

drivers/md/md.c

@@ -7415,6 +7415,7 @@ static int update_array_info(struct mddev *mddev, mdu_array_info_t *info)
 
 				mddev->bitmap_info.nodes = 0;
 				md_cluster_ops->leave(mddev);
+				module_put(md_cluster_mod);
 				mddev->safemode_delay = DEFAULT_SAFEMODE_DELAY;
 			}
 			mddev_suspend(mddev);