drm/i915/gt: Suppress warnings for unused debugging locals

With debugging turned off, we have to tell the compiler not to warn
about the unused debug locals.
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200213081217.3107410-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/gt/intel_lrc.c

@@ -2331,8 +2331,10 @@ static void process_csb(struct intel_engine_cs *engine)
 			if (GEM_SHOW_DEBUG() &&
 			    !i915_request_completed(*execlists->active) &&
 			    !reset_in_progress(execlists)) {
-				struct i915_request *rq = *execlists->active;
-				const u32 *regs = rq->context->lrc_reg_state;
+				struct i915_request *rq __maybe_unused =
+					*execlists->active;
+				const u32 *regs __maybe_unused =
+					rq->context->lrc_reg_state;
 
 				ENGINE_TRACE(engine,
 					     "ring:{start:0x%08x, head:%04x, tail:%04x, ctl:%08x, mode:%08x}\n",