quota: Convert dqio_mutex to rwsem

Convert dqio_mutex to rwsem and call it dqio_sem. No functional changes
yet.

Signed-off-by: Jan Kara <jack@suse.cz>
diff --git a/fs/super.c b/fs/super.c
index 6bc3352..221cfa1 100644
--- a/fs/super.c
+++ b/fs/super.c
@@ -242,7 +242,7 @@
 	atomic_set(&s->s_active, 1);
 	mutex_init(&s->s_vfs_rename_mutex);
 	lockdep_set_class(&s->s_vfs_rename_mutex, &type->s_vfs_rename_key);
-	mutex_init(&s->s_dquot.dqio_mutex);
+	init_rwsem(&s->s_dquot.dqio_sem);
 	s->s_maxbytes = MAX_NON_LFS;
 	s->s_op = &default_op;
 	s->s_time_gran = 1000000000;