drm/i915: Show the DPCD read error inline

When reporting the DPCD dump through debugfs, show the errors inline
where appropriate. If a read at one particular offset fails, report it.

Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=106371Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181010081706.29931-1-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_debugfs.c

@@ -4915,13 +4915,10 @@ static int i915_dpcd_show(struct seq_file *m, void *data)
 			continue;
 
 		err = drm_dp_dpcd_read(&intel_dp->aux, b->offset, buf, size);
-		if (err <= 0) {
-			DRM_ERROR("dpcd read (%zu bytes at %u) failed (%zd)\n",
-				  size, b->offset, err);
-			continue;
-		}
-
-		seq_printf(m, "%04x: %*ph\n", b->offset, (int) size, buf);
+		if (err < 0)
+			seq_printf(m, "%04x: ERROR %d\n", b->offset, (int)err);
+		else
+			seq_printf(m, "%04x: %*ph\n", b->offset, (int)err, buf);
 	}
 
 	return 0;