USB: gadget: f_rndis: Add check before queuing notification available

There is a chance that rndis_response_available() and unbind() race each
other due to which request's buffer might have freed and could cause
accessing freed buffer pointer. Hence add check before accessing buffer
pointer of USB request for interrupt endpoint.

CRs-fixed: 731323
Change-Id: I2082e54cbdc28817651e75e8e8ed13d0ee61a6d5
Signed-off-by: Vijayavardhan Vennapusa <vvreddy@codeaurora.org>
Merge "USB: gadget: f_rndis: Add check before queuing notification available"
Merge 240e7c0d2a29d067b4bb99f55754b6a4321bd387 on remote branch

Change-Id: If3b5a3203bd38b0feb7b2ca6242e267143ca2196
Merge "Merge 240e7c0d2a29d067b4bb99f55754b6a4321bd387 on remote branch"