sound: usb: Populate QMI request receive time stamp

t_request_recvd of uaudio_qmi_svc structure is not set
with a time stamp value. This results into incorrect
time delta getting printed at the end of the QMI response
being sent. Set the time stamp value at the entry of
handle_uaudio_stream_req().

Change-Id: If897b61fe8c5c62b558b9a277a6c1534efd59c95
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>