xa_close leaks xdisk_lk and releases wrong lock on raced-destruction defensive paths

Summary

Two defensive early-return paths in xa_close copied from xa_open but mistyped: both return while still holding xdisk_lk and terminating-path branch releases sc->lk (never acquired) instead of xdisk_lk. Result: leaked exclusive xdisk_lk deadlocking every subsequent xdisk operation OR lockmgr corruption/panic from releasing unowned lock. Correct pattern visible in xa_open lines 703-715.