ibmvnic: Fix TX completion error handling

[ Upstream commit ba246c175116e2e8fa4fdfa5f8e958e086a9a818 ]

TX completions received with an error return code are not
being processed properly. When an error code is seen, do not
proceed to the next completion before cleaning up the existing
entry's data structures.

Fixes: 032c5e82 ("Driver for IBM System i/p VNIC protocol")
Signed-off-by: Thomas Falcon <tlfalcon@linux.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>