This patch implement relative MCR/MSR function, such like
tiocmget()/tiocmset()/dtr_rts()/carrier_raised()

original f81232_carrier_raised() compared with wrong value UART_DCD.
It's should compared with UART_MSR_DCD.
Signed-off-by: Peter Hung <hpeter+linux_kernel@gmail.com>
Signed-off-by: Johan Hovold <johan@kernel.org>