drm/xe/oa: Destroy the stream_lock mutex

The mutex allocated in xe_oa_stream_init() was never previously
destroyed. Do so now.

Fixes: e936f885 ("drm/xe/oa/uapi: Expose OA stream fd")
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Reviewed-by: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240628052125.1847989-1-ashutosh.dixit@intel.com