AP_Motors: Use the same limits described in the wiki

According to Leonard Hall's tuning instructions at:
https://ardupilot.org/copter/docs/tuning-process-instructions.html
Fix a typo

libraries/AP_Motors/AP_MotorsMulticopter.cpp

@@ -51,7 +51,7 @@ const AP_Param::GroupInfo AP_MotorsMulticopter::var_info[] = {
 
     // @Param: BAT_VOLT_MAX
     // @DisplayName: Battery voltage compensation maximum voltage
-    // @Description: Battery voltage compensation maximum voltage (voltage above this will have no additional scaling effect on thrust).  Recommend 4.4 * cell count, 0 = Disabled
+    // @Description: Battery voltage compensation maximum voltage (voltage above this will have no additional scaling effect on thrust).  Recommend 4.2 * cell count, 0 = Disabled
     // @Range: 6 53
     // @Units: V
     // @User: Advanced
@@ -59,7 +59,7 @@ const AP_Param::GroupInfo AP_MotorsMulticopter::var_info[] = {
 
     // @Param: BAT_VOLT_MIN
     // @DisplayName: Battery voltage compensation minimum voltage
-    // @Description: Battery voltage compensation minimum voltage (voltage below this will have no additional scaling effect on thrust).  Recommend 3.5 * cell count, 0 = Disabled
+    // @Description: Battery voltage compensation minimum voltage (voltage below this will have no additional scaling effect on thrust).  Recommend 3.3 * cell count, 0 = Disabled
     // @Range: 6 42
     // @Units: V
     // @User: Advanced
@@ -84,7 +84,7 @@ const AP_Param::GroupInfo AP_MotorsMulticopter::var_info[] = {
     AP_GROUPINFO("PWM_TYPE", 15, AP_MotorsMulticopter, _pwm_type, PWM_TYPE_NORMAL),
 
     // @Param: PWM_MIN
-    // @DisplayName: PWM output miniumum
+    // @DisplayName: PWM output minimum
     // @Description: This sets the min PWM output value in microseconds that will ever be output to the motors, 0 = use input RC3_MIN
     // @Units: PWM
     // @Range: 0 2000