tty/serial: mpc52xx_uart: Don't zero port->sysrq

uart_handle_sysrq_char() already does it.

Signed-off-by: Dmitry Safonov <dima@arista.com>
Link: https://lore.kernel.org/r/20191213000657.931618-25-dima@arista.com


Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>