drm/xe/uc: Don't emit false error if running in execlist mode

When running in execlist mode (using force_execlist=1 modparam)
we incorrectly select the error path in xe_uc_init(), leading to
an unwanted error message like this:

[ ] xe 0000:00:00.0: [drm] *ERROR* GT0: Failed to initialize uC (0000000000000000)

Fix that by doing early return like we do in other similar cases.

Signed-off-by: Michal Wajdeczko <michal.wajdeczko@intel.com>
Cc: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Reviewed-by: Daniele Ceraolo Spurio <daniele.ceraolospurio@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20240521114857.712-1-michal.wajdeczko@intel.com