usb: gadget: qc_ecm: Remove clearing USB endpoint pointers

Clearing these endpoint pointers causes bam_data_connect()
to not execute the disconnect sequence properly and
not disable these endpoints.
This fix also clear cdev and func pointers after
bam_data_disconnect().

Change-Id: If93b5ac2a76b6479aad70f37cf15ee11924238f9
Signed-off-by: Bar Weiner <bweiner@codeaurora.org>