Copter: fixed off-by-one in rcmapper

oops ...

ArduCopter/radio.pde

@@ -122,12 +122,12 @@ static void read_radio()
         ap_system.new_radio_frame = true;
         uint16_t periods[8];
         hal.rcin->read(periods,8);
-        g.rc_1.set_pwm(periods[rcmap.roll()]);
-        g.rc_2.set_pwm(periods[rcmap.pitch()]);
+        g.rc_1.set_pwm(periods[rcmap.roll()-1]);
+        g.rc_2.set_pwm(periods[rcmap.pitch()-1]);
 
-        set_throttle_and_failsafe(periods[rcmap.throttle()]);
+        set_throttle_and_failsafe(periods[rcmap.throttle()-1]);
 
-        g.rc_4.set_pwm(periods[rcmap.yaw()]);
+        g.rc_4.set_pwm(periods[rcmap.yaw()-1]);
         g.rc_5.set_pwm(periods[4]);
         g.rc_6.set_pwm(periods[5]);
         g.rc_7.set_pwm(periods[6]);