aio-dio-append-write-fallocate-race: fix directio buffer alignment bugs

This program fails on filesystems where the stat() block size isn't a
strict power of two because it foolishly feeds that to posix_memalign to
allocate an aligned memory buffer for directio.  posix_memalign requires
the alignment value to be a power of two, so generic/586 fails.

The system page size generally works well for directio buffers, so use
that instead.

Signed-off-by: Darrick J. Wong <djwong@kernel.org>
Reviewed-by: Christoph Hellwig <hch@lst.de>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

src/aio-dio-regress/aio-dio-append-write-fallocate-race.c

@@ -65,7 +65,7 @@ test(
 	}
 	blocksize = sbuf.st_blksize;
 
-	ret = posix_memalign((void **)&buf, blocksize, blocksize);
+	ret = posix_memalign((void **)&buf, sysconf(_SC_PAGESIZE), blocksize);
 	if (ret) {
 		errno = ret;
 		perror("buffer");