drivers/tty/serial/mpc52xx_uart.c: fix typo in C comment

Fix reference on PPC_MPC52xx in C comment after #endif.

Signed-off-by: Valentin Rothberg <valentinrothberg@gmail.com>
Reviewed-by: Peter Hurley <peter@hurleysoftware.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>