ide: don't call memcpy with the same source and destination

The parisc architecture recently reimplemented the memcpy function and
their reimplementation crashed when source and destination overlapped.

The crash happened in the function ide_complete_cmd where memcpy is called
with the same source and destination pointer. According to the C
specification, memcpy behavior is undefined if the source and destination
range overlaps. This patches fixes the undefined behavior.

Signed-off-by: Mikulas Patocka <mpatocka@redhat.com>
Reviewed-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Signed-off-by: David S. Miller <davem@davemloft.net>