rndis_wlan: add return value validation

[ Upstream commit 9dc7efd3978aa67ae598129d2a3f240b390ce508 ]

Function create_singlethread_workqueue() will return a NULL pointer if
there is no enough memory, and its return value should be validated
before using. However, in function rndis_wlan_bind(), its return value
is not checked. This may cause NULL dereference bugs. This patch fixes
it.

Signed-off-by: Pan Bian <bianpan2016@163.com>
Signed-off-by: Kalle Valo <kvalo@codeaurora.org>
Signed-off-by: Sasha Levin <alexander.levin@microsoft.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>