usb: gadget: gps: Handle case when response queue is empty

When there is no packet available in response queue on device
side and host requests for GET_ENCAPSULATED response on control
endpoint, gps_setup() API returns as -EOPNOTSUPP. This results
into controller driver stalling EP0 OUT endpoint which host
side driver may not expected. Hence to avoid this stalling of
EP0 OUT endpoint returns zero instead of -EOPNOTSUPP from
gps_setup() API.

Also use pr_debug() instead of pr_err() when there is no control
response packet available as it is not actual error but condition
where there is no data available to send.

CRs-Fixed: 995861
Change-Id: I6ac58ba5d1cb895f5d49e5df3f4d7257dc9a628c
Signed-off-by: Mayank Rana <mrana@codeaurora.org>