f_gsi: Fix error handling with usb_func_ep_queue() return value

usb_func_ep_queue() returns -EAGAIN if usb is function suspended and
successfully remote wakeup is performed. This change fixes error
handling with USB GSI function driver to make sure caller knows that
request is actually queued or not from this context. This makes sure
that USB request is queued once USB host has resumed USB bus.

CRs-Fixed: 1033093
Change-Id: I3f3cb1b6b42530bfa93e0d4badacfe651b6bbb4c
Signed-off-by: Mayank Rana <mrana@codeaurora.org>