net: qualcomm: rmnet: move null check on dev before dereferecing it

net: qualcomm: rmnet: move null check on dev before dereferecing it

[ Upstream commit 3c18aa1464f9232d6abac8d7b4540f61b0658d62 ]

Currently dev is dereferenced by the call dev_net(dev) before dev is null
checked.  Fix this by null checking dev before the potential null
pointer dereference.

Detected by CoverityScan, CID#1462955 ("Dereference before null check")

Fixes: 23790ef12082 ("net: qualcomm: rmnet: Allow to configure flags for existing devices")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>