drm/i915: Fix memory leaks in function live_nop_switch

Be sure to properly free the allocated memory before exiting
the live_nop_switch function.

Signed-off-by: Cong Liu <liucong2@kylinos.cn>
Suggested-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230517050204.4111874-1-liucong2@kylinos.cn