platform/x86/intel/tpmi: convert mutex in mem_write() to guard

platform/x86/intel/tpmi: convert mutex in mem_write() to guard

Convert the explicit mutex_lock/mutex_unlock pair in mem_write() into
a cleanup.h guard(mutex)() scope-based lock acquisition. This removes
the remaining goto-based cleanup path and keeps the lock held until
the end of the mem_write() scope.

Suggested-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: ZhaoJinming <zhaojinming@uniontech.com>
Link: https://patch.msgid.link/20260521130848.2860219-2-zhaojinming@uniontech.com
Reviewed-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>
Signed-off-by: Ilpo Järvinen <ilpo.jarvinen@linux.intel.com>