ionic: catch failure from devlink_alloc

ionic: catch failure from devlink_alloc

Add a check for NULL on the alloc return.  If devlink_alloc() fails and
we try to use devlink_priv() on the NULL return, the kernel gets very
unhappy and panics. With this fix, the driver load will still fail,
but at least it won't panic the kernel.

Fixes: df69ba43217d ("ionic: Add basic framework for IONIC Network device driver")
Signed-off-by: Shannon Nelson <shannon.nelson@amd.com>
Reviewed-by: Simon Horman <simon.horman@corigine.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Signed-off-by: David S. Miller <davem@davemloft.net>