net: sparx5: switchdev: fix possible NULL pointer dereference

net: sparx5: switchdev: fix possible NULL pointer dereference

[ Upstream commit 0906f3a3df07835e37077d8971aac65347f2ed57 ]

As the possible failure of the allocation, devm_kzalloc() may return NULL
pointer.
Therefore, it should be better to check the 'db' in order to prevent
the dereference of NULL pointer.

Fixes: 10615907e9b51 ("net: sparx5: switchdev: adding frame DMA functionality")
Signed-off-by: Zheng Yongjun <zhengyongjun3@huawei.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>