atl1e: unmap partially mapped skb on dma error and free skb

[ Upstream commit 584ec4355355ffac43571b02a314d43eb2f7fcbf ]

Ben Hutchings pointed out that my recent update to atl1e
in commit 352900b583b2852152a1e05ea0e8b579292e731e
("atl1e: fix dma mapping warnings") was missing a bit of code.

Specifically it reset the hardware tx ring to its origional state when
we hit a dma error, but didn't unmap any exiting mappings from the
operation.  This patch fixes that up.  It also remembers to free the
skb in the event that an error occurs, so we don't leak.  Untested, as
I don't have hardware.  I think its pretty straightforward, but please
review closely.

Signed-off-by: Neil Horman <nhorman@tuxdriver.com>
CC: Ben Hutchings <bhutchings@solarflare.com>
CC: Jay Cliburn <jcliburn@gmail.com>
CC: Chris Snook <chris.snook@gmail.com>
CC: "David S. Miller" <davem@davemloft.net>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>