drm/i915/opregion: try to validate RVDA VBT only if it's there

Seems more sensible this way, and reduces indent for the more common
case.
Reviewed-by: Bob Paauwe <bob.j.paauwe@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1490783578-6065-2-git-send-email-jani.nikula@intel.com

drivers/gpu/drm/i915/intel_opregion.c

@@ -920,8 +920,8 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
 	char buf[sizeof(OPREGION_SIGNATURE)];
 	int err = 0;
 	void *base;
-	const void *vbt = NULL;
-	u32 vbt_size = 0;
+	const void *vbt;
+	u32 vbt_size;
 
 	BUILD_BUG_ON(sizeof(struct opregion_header) != 0x100);
 	BUILD_BUG_ON(sizeof(struct opregion_acpi) != 0x100);
@@ -984,21 +984,21 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
 					  MEMREMAP_WB);
 		vbt = opregion->rvda;
 		vbt_size = opregion->asle->rvds;
-	}
-
 		if (intel_bios_is_valid_vbt(vbt, vbt_size)) {
 			DRM_DEBUG_KMS("Found valid VBT in ACPI OpRegion (RVDA)\n");
 			opregion->vbt = vbt;
 			opregion->vbt_size = vbt_size;
-	} else {
+			goto out;
+		}
+	}
+
 	vbt = base + OPREGION_VBT_OFFSET;
 	/*
-		 * The VBT specification says that if the ASLE ext mailbox is
-		 * not used its area is reserved, but on some CHT boards the VBT
-		 * extends into the ASLE ext area. Allow this even though it is
-		 * against the spec, so we do not end up rejecting the VBT on
-		 * those boards (and end up not finding the LCD panel because of
-		 * this).
+	 * The VBT specification says that if the ASLE ext mailbox is not used
+	 * its area is reserved, but on some CHT boards the VBT extends into the
+	 * ASLE ext area. Allow this even though it is against the spec, so we
+	 * do not end up rejecting the VBT on those boards (and end up not
+	 * finding the LCD panel because of this).
 	 */
 	vbt_size = (mboxes & MBOX_ASLE_EXT) ?
 		OPREGION_ASLE_EXT_OFFSET : OPREGION_SIZE;
@@ -1008,7 +1008,6 @@ int intel_opregion_setup(struct drm_i915_private *dev_priv)
 		opregion->vbt = vbt;
 		opregion->vbt_size = vbt_size;
 	}
-	}
 
 out:
 	return 0;