fs: synchronize_rcu when unregister_filesystem success not failure

While checking unregister_filesystem for saftey vs extra calls for
"ext4: register ext2 and ext3 alias after ext4" I realized that
the synchronize_rcu() was called on the error path but not on
the success path.

Cc: stable (2.6.38)
Signed-off-by: Milton Miller <[e-mail]>
[ This probably won't really make a difference since commit d863b50ab013
("vfs: call rcu_barrier after ->kill_sb()"), but it's the right thing
to do. - Linus ]
Signed-off-by: Linus Torvalds <[e-mail]>

fs/filesystems.c

···
 			*tmp = fs->next;
 			fs->next = NULL;
 			write_unlock(&file_systems_lock);
+			synchronize_rcu();
 			return 0;
 		}
 		tmp = &(*tmp)->next;
 	}
 	write_unlock(&file_systems_lock);
-
-	synchronize_rcu();
 
 	return -EINVAL;
 }