Yours lsmod:
ftdi_sio 27200 0
usbserial 17633 1 ftdi_sio
Correct lsmod:
pl2303 6688 0
usbserial 17633 1 pl2303
opkg update
opkg remove kmod-usb-serial-ftdi
opkg remove kmod-usb-serial-pl2303
opkg install kmod-usb-serial-pl2303
lsmod