snic: Fix use-after-free in case of a dma mapping error

If there is a dma mapping error snic kfree()s buf right before printing
it.  Change the order to not accidently trip on memory that's not owned
by us anymore.

Signed-off-by: Johannes Thumshirn <jthumshirn@suse.de>
Acked-by: Narsimhulu Musini <nmusini@cisco.com>
Reviewed-by: Laurence Oberman <loberman@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>