negate values for js1_ud and js2_ud in read methods

refs 7795

org.fortiss.af3.platform.raspberry/trunk/lib/src/Gamepad.c

@@ -206,7 +206,7 @@ GEN_TYPE_double gp_btnLX_read() {
 }
 
 GEN_TYPE_double gp_btnLY_read() {
-    return ie.btns.js1_ud;
+    return -ie.btns.js1_ud;
 }
 
 GEN_TYPE_double gp_btnRX_read() {
@@ -214,7 +214,7 @@ GEN_TYPE_double gp_btnRX_read() {
 }
 
 GEN_TYPE_double gp_btnRY_read() {
-    return ie.btns.js2_ud;
+    return -ie.btns.js2_ud;
 }
 
 // noval