usb: gadget: uac2: Change synchronization type of data ep to SYNC

As per the UAC 2.0 specification, ASYNC data endpoint is required
to have feedback data endpoint. Since driver descriptor does not
include feedback data endpoint, change endpoint bmAttributes for
data endpoint to represent as SYNC instead of ASYNC. This allows
device to enumerate on windows 10 PC.

Change-Id: Ied3c2c94a8cd1cc130bb77484641f0d8d5ed642d
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>