usb: f_gps: Fix incorrect response available notifications

On function resume we notify response available to the
host even if there are no responses. Fix this by checking
the response queue on resume before notifying the host.

CRs-Fixed: 2098360
Change-Id: If49fc6c9722b2e4be514ae128f1803f0b0d90fb6
Signed-off-by: Sriharsha Allenki <sallenki@codeaurora.org>