drm/i915/guc: prefer 'dev_priv' to 'dev' for intra-module functions

There are four non-static functions in i915_guc_submission.c that take a
'dev' parameter. All are called only from GuC loader code, and can be
easily converted to accept 'dev_priv' instead.

Signed-off-by: Dave Gordon <david.s.gordon@intel.com>
Reviewed-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Signed-off-by: Tvrtko Ursulin <tvrtko.ursulin@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1465579766-31595-1-git-send-email-david.s.gordon@intel.com