target: copper: Add support to use updated pmic api.

Use the new volume down key detect api.
diff --git a/target/copper/init.c b/target/copper/init.c
index 71ccc96..dfbb23a 100644
--- a/target/copper/init.c
+++ b/target/copper/init.c
@@ -95,9 +95,10 @@
 }
 
 /* Return 1 if vol_down pressed */
-int target_volume_down()
+uint32_t target_volume_down()
 {
-	return pm8x41_vol_down_key_status();
+	/* Volume down button is tied in with RESIN on MSM8974. */
+	return pm8x41_resin_bark_workaround_status();
 }
 
 static void target_keystatus()