drm/i915/dsi: don't pass arbitrary data to sideband

Since sequence block v2 the second byte contains flags other than just
pull up/down. Don't pass arbitrary data to the sideband interface.

The rest may or may not work for sequence block v2, but there should be
no harm done.

Cc: stable@vger.kernel.org
Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: http://patchwork.freedesktop.org/patch/msgid/ebe3c2eee623afc4b3a134533b01f8d591d13f32.1454582914.git.jani.nikula@intel.com
(cherry picked from commit 4e1c63e3)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_dsi_panel_vbt.c

@@ -207,7 +207,7 @@ static const u8 *mipi_exec_gpio(struct intel_dsi *intel_dsi, const u8 *data)
 	gpio = *data++;
 
 	/* pull up/down */
-	action = *data++;
+	action = *data++ & 1;
 
 	if (gpio >= ARRAY_SIZE(gtable)) {
 		DRM_DEBUG_KMS("unknown gpio %u\n", gpio);