usb: gadget: Reset notify count to 0 upon completion for RNDIS

When host RNDIS sends reset message it skips response available
notification and directly sends get encap response. This causes
notify count to become > 1. As a result when notify completion happens
driver is queuing another notify response available when there is
no legitimate response to send from device side. Hence reset notify
count back to 0 after the completion of notify response, so that
next notification will only be sent when there is a send encap
command sent by host.

Change-Id: I242478408f8cb60fb5af5c741dbf2e8bf3e38af8
Signed-off-by: Hemant Kumar <hemantk@codeaurora.org>