dwc3: gadget: Don't memset TRB ring with zero related to USB GSI endpoint

USB GSI endpoint related TRB ring is allocated with EP_OPS. Each USB
endpoint related TRB ring is zeroed with usb_ep_disable() operation. Hence
if USB composition switch or USB cable disconnect is performed when there
is active data transfer with USB GSI endpoint, it results into IPA GSI
accessing 0x0 address causing bus errors. Hence fix this issue by not
memsetting TRB ring with zero for USB GSI endpoint.

CRs-Fixed: 1072782
Change-Id: I92df514e31d5168b8dff4b249f4d8fd3e70c0118
Signed-off-by: Mayank Rana <mrana@codeaurora.org>