ANDROID: extcon: Export symbol of `extcon_get_edev_name`

usb-dwc3-msm module call this function which is located in
`drivers/usb/dwc3/dwc3-msm.c`.

Export function so the module can be built.

Bug: 157994070
Signed-off-by: lucaswei <lucaswei@google.com>
Change-Id: Ie7fd78ea7188a96d08a8b7bf4c0e146536f20fe1