ixgbe: fix possible null buffer error

ixgbe: fix possible null buffer error

commit b811ce9104a7f7663ddae4f7795a194a103b8f90 upstream.

It seems that at least one PPC machine would occasionally give a (valid) 0 as
the return value from dma_map, this caused the ixgbe code to not work
correctly.  A fix is pending in the PPC tree to not return 0 from dma map, but
we can also fix the driver to make sure we don't mess up in other arches as
well.

This patch is applicable to all current stable kernels.

Ref: https://bugzilla.redhat.com/show_bug.cgi?id=683611

Reported-by: Neil Horman <nhorman@redhat.com>
Signed-off-by: Jesse Brandeburg <jesse.brandeburg@intel.com>
CC: Alexander Duyck <alexander.h.duyck@intel.com>
Tested-by: Thadeu Lima de Souza Cascardo <cascardo@linux.vnet.ibm.com>
Tested-by: Phil Schmitt <phillip.j.schmitt@intel.com>
Signed-off-by: Jeff Kirsher <jeffrey.t.kirsher@intel.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>