tty: omap-serial: Fix initial on-boot RTS GPIO level

The rs485 flag "SER_RS485_RTS_AFTER_SEND" was wrongly read from the GPIO
flags. This caused the RTS pin to be high during boot.

Signed-off-by: Rafael Gago Castano <rgc@hms.se>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>