qlcnic: Avoid potential NULL pointer dereference

[ Upstream commit 5bf7295fe34a5251b1d241b9736af4697b590670 ]

netdev_alloc_skb can fail and return a NULL pointer which is
dereferenced without a check. The patch avoids such a scenario.

Signed-off-by: Aditya Pakki <pakki001@umn.edu>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin (Microsoft) <sashal@kernel.org>