drm/i915: Avoid compiler warning for maybe unused gu_misc_iir

/kisskb/src/drivers/gpu/drm/i915/i915_irq.c: warning: 'gu_misc_iir' may be used uninitialized in this function [-Wuninitialized]:  => 3120:10

Silence the compiler warning by ensuring that the local variable is
initialised and removing the guard that is confusing the older gcc.
Reported-by: Geert Uytterhoeven <geert@linux-m68k.org>
Fixes: df0d28c1 ("drm/i915/icl: GSE interrupt moves from DE_MISC to GU_MISC")
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Cc: Paulo Zanoni <paulo.r.zanoni@intel.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180926104718.17462-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_irq.c

@@ -3088,36 +3088,27 @@ gen11_gt_irq_handler(struct drm_i915_private * const i915,
 	spin_unlock(&i915->irq_lock);
 }
 
-static void
-gen11_gu_misc_irq_ack(struct drm_i915_private *dev_priv, const u32 master_ctl,
-		      u32 *iir)
+static u32
+gen11_gu_misc_irq_ack(struct drm_i915_private *dev_priv, const u32 master_ctl)
 {
 	void __iomem * const regs = dev_priv->regs;
+	u32 iir;
 
 	if (!(master_ctl & GEN11_GU_MISC_IRQ))
-		return;
+		return 0;
+
+	iir = raw_reg_read(regs, GEN11_GU_MISC_IIR);
+	if (likely(iir))
+		raw_reg_write(regs, GEN11_GU_MISC_IIR, iir);
 
-	*iir = raw_reg_read(regs, GEN11_GU_MISC_IIR);
-	if (likely(*iir))
-		raw_reg_write(regs, GEN11_GU_MISC_IIR, *iir);
+	return iir;
 }
 
 static void
-gen11_gu_misc_irq_handler(struct drm_i915_private *dev_priv,
-			  const u32 master_ctl, const u32 iir)
+gen11_gu_misc_irq_handler(struct drm_i915_private *dev_priv, const u32 iir)
 {
-	if (!(master_ctl & GEN11_GU_MISC_IRQ))
-		return;
-
-	if (unlikely(!iir)) {
-		DRM_ERROR("GU_MISC iir blank!\n");
-		return;
-	}
-
 	if (iir & GEN11_GU_MISC_GSE)
 		intel_opregion_asle_intr(dev_priv);
-	else
-		DRM_ERROR("Unexpected GU_MISC interrupt 0x%x\n", iir);
 }
 
 static irqreturn_t gen11_irq_handler(int irq, void *arg)
@@ -3154,12 +3145,12 @@ static irqreturn_t gen11_irq_handler(int irq, void *arg)
 		enable_rpm_wakeref_asserts(i915);
 	}
 
-	gen11_gu_misc_irq_ack(i915, master_ctl, &gu_misc_iir);
+	gu_misc_iir = gen11_gu_misc_irq_ack(i915, master_ctl);
 
 	/* Acknowledge and enable interrupts. */
 	raw_reg_write(regs, GEN11_GFX_MSTR_IRQ, GEN11_MASTER_IRQ | master_ctl);
 
-	gen11_gu_misc_irq_handler(i915, master_ctl, gu_misc_iir);
+	gen11_gu_misc_irq_handler(i915, gu_misc_iir);
 
 	return IRQ_HANDLED;
 }