md-cluster: Fix a memleak in an error handling path

md-cluster: Fix a memleak in an error handling path

We know that 'bm_lockres' is NULL here, so 'lockres_free(bm_lockres)' is a
no-op. According to resource handling in case of error a few lines below,
it is likely that 'bitmap_free(bitmap)' was expected instead.

Fixes: b98938d16a10 ("md-cluster: introduce cluster_check_sync_size")
Signed-off-by: Christophe JAILLET <christophe.jaillet@wanadoo.fr>
Reviewed-by: Guoqing Jiang <gqjiang@suse.com>
Signed-off-by: Shaohua Li <shli@fb.com>