drm/i915/guc: Remove bogus null check

This null check is bogus because we are already using 'ce' stuff
in many places before this function is called.

Having this here is useless and confuses static analyzer tools
that can see:

struct intel_engine_cs *engine = ce->engine;

before this check, in the same function.

Reported-by: kernel test robot <lkp@intel.com>
Reported-by: Dan Carpenter <dan.carpenter@linaro.org>
Closes: https://lore.kernel.org/r/202403101225.7AheJhZJ-lkp@intel.com/
Cc: Vinay Belgaumkar <vinay.belgaumkar@intel.com>
Cc: John Harrison <John.C.Harrison@Intel.com>
Reviewed-by: Andi Shyti <andi.shyti@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240328213107.90632-1-rodrigo.vivi@intel.com
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>