usb: gadget: f_mbim: Set bnotification type in mbim_write

Fix mbim usb notify callback when ep_queue is used.
With this change, mbim interface on host coming up
and working properly.

Change-Id: I3743d48b722bff060814e05799885a0e5193e27c
Signed-off-by: Prasadarao Durvasula <pdurvasu@codeaurora.org>
Signed-off-by: Sivasri Kumar Vanka <sivasri@codeaurora.org>