drm: Fix documentation generation for DP_DPCD_QUIRK_NO_PSR

The DP_DPCD_QUIRK_NO_PSR comment is missing colon causing this
warning when generating kernel documentation.

./include/drm/drm_dp_helper.h:1374: warning: Incorrect use of kernel-doc format:          * @DP_DPCD_QUIRK_NO_PSR

Fixes: 7c5c641a (drm/i915: Disable PSR in Apple panels)
Cc: Dhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Signed-off-by: NJosé Roberto de Souza <jose.souza@intel.com>
Reviewed-by: NDhinakaran Pandiyan <dhinakaran.pandiyan@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20181205184850.13218-1-jose.souza@intel.com

include/drm/drm_dp_helper.h

@@ -1370,7 +1370,7 @@ enum drm_dp_quirk {
 	 */
 	DP_DPCD_QUIRK_CONSTANT_N,
 	/**
-	 * @DP_DPCD_QUIRK_NO_PSR
+	 * @DP_DPCD_QUIRK_NO_PSR:
 	 *
 	 * The device does not support PSR even if reports that it supports or
 	 * driver still need to implement proper handling for such device.