allow vmsplice to work in 32-bit mode on ppc64

Trivial change to pass vmsplice arguments through the compat layer on
pp64.

Signed-off-by: Don Zickus <dzickus@redhat.com>
Acked-by: Stephen Rothwell <sfr@canb.auug.org.au>
Acked-by: Paul Mackerras <paulus@samba.org>
Cc: Benjamin Herrenschmidt <benh@kernel.crashing.org>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Linus Torvalds <torvalds@linux-foundation.org>