Update Split-AzReservation.md (#15049)

I have changed the quantity command in ### Example 1

Author: Srihsu

src/Reservations/Reservations/help/Split-AzReservation.md

@@ -31,7 +31,7 @@ Split a `Reservation` into two `Reservation`s with specified quantity distributi
 
 ### Example 1
 ```
-PS C:\> Split-AzReservation -ReservationOrderId "00000000-ffff-ffff-0000-00000fffff" -ReservationId "11111111-1111-1111-1111-1111111111" -Quantities 2,3
+PS C:\> Split-AzReservation -ReservationOrderId "00000000-ffff-ffff-0000-00000fffff" -ReservationId "11111111-1111-1111-1111-1111111111" -Quantity 2,3
 ```
 
 Split the specified `Reservation` into two `Reservation`s with the corresponding quantities