staging: fsl-dpaa2/eth: Fix incorrect kfree

Use netdev_alloc_frag() instead of kmalloc to allocate space for
the S/G table of egress multi-buffer frames.

This fixes a bug where an unaligned pointer received from the
allocator would be overwritten with the 64B aligned value,
leading to a wrong address being later passed to kfree.

Signed-off-by: Ioana Radulescu <ruxandra.radulescu@nxp.com>
Reported-by: Dan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>