ieee1394: raw1394: add sparse annotations to raw1394_compat_write

Eliminate the following warnings in raw1394_compat_write()'s error
return path, seen on x86-64 with CONFIG_COMPAT=y:

drivers/ieee1394/raw1394.c:381:17: warning: incorrect type in return expression (different address spaces)
drivers/ieee1394/raw1394.c:381:17:    expected char const [noderef] <asn:1>*
drivers/ieee1394/raw1394.c:381:17:    got void *
drivers/ieee1394/raw1394.c:2252:14: warning: incorrect type in argument 1 (different address spaces)
drivers/ieee1394/raw1394.c:2252:14:    expected void const *ptr
drivers/ieee1394/raw1394.c:2252:14:    got char const [noderef] <asn:1>*[assigned] buffer
drivers/ieee1394/raw1394.c:2253:19: warning: incorrect type in argument 1 (different address spaces)
drivers/ieee1394/raw1394.c:2253:19:    expected void const *ptr
drivers/ieee1394/raw1394.c:2253:19:    got char const [noderef] <asn:1>*[assigned] buffer

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