drm/i915/uc: do not free err log on uc_fini

We need to keep the GuC error logs around to debug the load failure,
so we can't clean them in the error unwind, which includes uc_fini().
Moving the cleanup to driver remove ensures that the logs stick around
long enough for us to dump them.

v2: reword commit msg (John)

Signed-off-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Cc: Michal Wajdeczko <michal.wajdeczko@intel.com>
Reviewed-by: John Harrison <John.C.Harrison@Intel.com>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200326181121.16869-7-daniele.ceraolospurio@intel.com