serial: ucc_uart: make qe_uart_set_mctrl() static

This eliminates the following sparse warning:

drivers/tty/serial/ucc_uart.c:286:6: warning: symbol 'qe_uart_set_mctrl'
was not declared. Should it be static?

Reported-by: Hulk Robot <hulkci@huawei.com>
Acked-by: Jiri Slaby <jirislaby@kernel.org>
Signed-off-by: Jason Yan <yanaijie@huawei.com>
Link: https://lore.kernel.org/r/20200912033834.143166-1-yanaijie@huawei.com


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