drm/i915: Don't attempt to read an unitialized stack value

If intel_sdvo_get_value() fails here, val is unitialized and the cross
check will compare the pipe config multiplier with a bogus value.

Instead, only set encoder_pixel_multiplier when the sdvo command has
been successful. The cross check will compare the pipe config value with
0 otherwise.

v2: Do the cross check with the initial value of encoder_pixel_multiplier (0)
if the sdvo command fails (and thus keep the warning) (Daniel Vetter)
Signed-off-by: Damien Lespiau <damien.lespiau@intel.com>
Signed-off-by: Daniel Vetter <daniel.vetter@ffwll.ch>

drivers/gpu/drm/i915/intel_sdvo.c

@@ -1357,7 +1357,8 @@ static void intel_sdvo_get_config(struct intel_encoder *encoder,
 	}
 
 	/* Cross check the port pixel multiplier with the sdvo encoder state. */
-	intel_sdvo_get_value(intel_sdvo, SDVO_CMD_GET_CLOCK_RATE_MULT, &val, 1);
+	if (intel_sdvo_get_value(intel_sdvo, SDVO_CMD_GET_CLOCK_RATE_MULT,
+				 &val, 1)) {
 		switch (val) {
 		case SDVO_CLOCK_RATE_MULT_1X:
 			encoder_pixel_multiplier = 1;
@@ -1369,6 +1370,7 @@ static void intel_sdvo_get_config(struct intel_encoder *encoder,
 			encoder_pixel_multiplier = 4;
 			break;
 		}
+	}
 
 	WARN(encoder_pixel_multiplier != pipe_config->pixel_multiplier,
 	     "SDVO pixel multiplier mismatch, port: %i, encoder: %i\n",