usb: dwc3: debugfs: Add missing in_lpm check

dwc->in_lpm check is missing from dwc3_tx_request_queue_show
function. Calling it can lead to unclocked access of DWC3
register. Fix it by adding the missing check.

Change-Id: I7fac7f3bc0187636b7bc79dd241ec5fa29aa648c
Signed-off-by: Ajay Agarwal <ajaya@codeaurora.org>