ieee1394: raw1394: Add ioctl() for 32bit userland on 64bit kernel, amendment

Pointed out by Arnd Bergmann:  PPC32 aligns this at 64bit, IA32 packs
it.  A kernel-wide available __compat_u64 which is 4-byte aligned on
AMD64 and IA64 would be nicer though.

Signed-off-by: Stefan Richter <stefanr@s5r6.in-berlin.de>