net: dlink: handle dma_map_single() failure properly

[ Upstream commit 65946eac ]

There is no error handling for `dma_map_single()` failures.

Add error handling by checking `dma_mapping_error()` and freeing
the `skb` using `dev_kfree_skb()` (process context) when it fails.

Fixes: 1da177e4 ("Linux-2.6.12-rc2")
Signed-off-by: Yeounsu Moon <yyyynoom@gmail.com>
Tested-on: D-Link DGE-550T Rev-A3
Suggested-by: Simon Horman <horms@kernel.org>
Reviewed-by: Simon Horman <horms@kernel.org>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Sasha Levin <sashal@kernel.org>