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>