drm/xe/oa: Fix potential NPD when OA is not initialized

If oa->xe can be NULL then we shall not use it as a valid pointer.

Fixes: cdf02fe1 ("drm/xe/oa/uapi: Add/remove OA config perf ops")
Fixes: b6fd51c6 ("drm/xe/oa/uapi: Define and parse OA stream properties")
Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
Cc: Ashutosh Dixit <ashutosh.dixit@intel.com>
Cc: Umesh Nerlige Ramappa <umesh.nerlige.ramappa@intel.com>
Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Reviewed-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Signed-off-by: Ashutosh Dixit <ashutosh.dixit@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240619175427.861-1-michal.wajdeczko@intel.com