mtkmodem: rename struct mtk_data instances to md

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
mtkmodem: rename GRil instances to ril

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
mtkmodem: rename struct ofono_modem instances to modem

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
rilmodem: rename struct ril_data instances to rd

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>
rilmodem: rename GRil instances to ril

Signed-off-by: You-Sheng Yang <vicamo@gmail.com>