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: 90198355b83c ("drm/i915/dsi: Add DCS control for Panel PWM")
Cc: Jani Nikula <[e-mail]>
Cc: Daniel Vetter <[e-mail]>
Cc: Yetunde Adebisi <[e-mail]>
Cc: Deepak M <[e-mail]>
Cc: Jani Nikula <[e-mail]>
Signed-off-by: Balasubramaniam, Hari Chand <[e-mail]>
Reviewed-by: Jani Nikula <[e-mail]>
Signed-off-by: Jani Nikula <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/[e-mail]
(cherry picked from commit d59814a5b4852442e1d03c569a4542f8b08356a7)
Signed-off-by: Jani Nikula <[e-mail]>

drivers/gpu/drm/i915/intel_dsi_dcs_backlight.c

···
 	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 */