usb: gadget: f_mbim: Acquire spin lock before calling mbim_do_notify()

commit e9df68ad (usb: gadget: f_mbim: Queue notification request upon
function resume) called mbim_do_notify() upon resume to queue notification
request without taking spin lock. This results into spin lock BUG
because the API expects caller to take the lock. Hence fix the issue
by taking spin lock before calling this API upon function resume.

Change-Id: Ic4eb7c9ce27edbfce61d58b7cbdb0a67e6a40c17
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>