drm/xe/reg_sr: Fix leak on xa_store failure

drm/xe/reg_sr: Fix leak on xa_store failure

Free the newly allocated entry when xa_store() fails to avoid a memory
leak on the error path.

v2: use goto fail_free. (Bala)

Fixes: e5283bd4dfec ("drm/xe/reg_sr: Remove register pool")
Cc: Balasubramani Vivekanandan <balasubramani.vivekanandan@intel.com>
Cc: Matt Roper <matthew.d.roper@intel.com>
Signed-off-by: Shuicheng Lin <shuicheng.lin@intel.com>
Reviewed-by: Matt Roper <matthew.d.roper@intel.com>
Link: https://patch.msgid.link/20260204172810.1486719-2-shuicheng.lin@intel.com
Signed-off-by: Matt Roper <matthew.d.roper@intel.com>