drm/i915: Initialize 'data' in intel_dsi_dcs_backlight.c

variable 'data' may be used uninitialized in this function. thus,
'function dcs_get_backlight' will return unwanted value/fail.

Thus, adding NULL initialized to 'data' variable will solve the return
failure happening.

v2: Change commit message to reflect upstream with proper message

Fixes: 90198355 ("drm/i915/dsi: Add DCS control for Panel PWM")
Cc: Jani Nikula <jani.nikula@intel.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Yetunde Adebisi <yetundex.adebisi@intel.com>
Cc: Deepak M <m.deepak@intel.com>
Cc: Jani Nikula <jani.nikula@linux.intel.com>
Signed-off-by: Balasubramaniam, Hari Chand <hari.chand.balasubramaniam@intel.com>
Reviewed-by: Jani Nikula <jani.nikula@intel.com>
Signed-off-by: Jani Nikula <jani.nikula@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/1502762746-191826-1-git-send-email-hari.chand.balasubramaniam@intel.com
(cherry picked from commit d59814a5)
Signed-off-by: Jani Nikula <jani.nikula@intel.com>

drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c

@@ -46,7 +46,7 @@ static u32 dcs_get_backlight(struct intel_connector *connector)
 	struct intel_encoder *encoder = connector->encoder;
 	struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base);
 	struct mipi_dsi_device *dsi_device;
-	u8 data;
+	u8 data = 0;
 	enum port port;
 
 	/* FIXME: Need to take care of 16 bit brightness level */