An AIO read or write should return -EINVAL if the offset is negative.
This check matches the one in pread and pwrite.

This was found by the libaio test suite.
Signed-off-by: NRusty Russell <rusty@rustcorp.com.au>
Acked-by: NZach Brown <zach.brown@oracle.com>
Signed-off-by: NAndrew Morton <akpm@linux-foundation.org>
Signed-off-by: NLinus Torvalds <torvalds@linux-foundation.org>