intel_th: msu: Fix possible memory leak in mode_store()

'mode' is malloced in mode_store() and should be freed before leaving
from the error handling cases, otherwise it will cause memory leak.

Fixes: 615c164d ("intel_th: msu: Introduce buffer interface")
Signed-off-by: Wei Yongjun <weiyongjun1@huawei.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
Link: https://lore.kernel.org/lkml/20190801013825.182543-1-weiyongjun1@huawei.com/
Link: https://lore.kernel.org/r/20191028070651.9770-6-alexander.shishkin@linux.intel.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>