usb: gadget: f_rmnet: Fix ctrl device creation for rmnet

With moving from misc device to character device the
rment_ctrl and the dpl_ctrl were not populated under
/dev. Fix this by properly assigning the module name
and while at it fix the incorrect usage of
file->driverdata to get the qti_ctrl_port.

Change-Id: Ic916208cefd79a728a58a32fb20f428d51eddea5
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>