i915/HuC: Add an extra check for platforms that do not have HUC

Return silently without producing much noise on platforms
that have a HuC but the firmware is absent.

Cc: Ander Conselvan De Oliveira <ander.conselvan.de.oliveira@intel.com>
Cc: Rodrigo Vivi <rodrigo.vivi@itel.com>
Signed-off-by: Anusha Srivatsa <anusha.srivatsa@intel.com>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@gmail.com>
Signed-off-by: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1488398335-13121-1-git-send-email-anusha.srivatsa@intel.com