fs/affs: bugfix: Write files greater than page size on OFS

Previous AFFS patch fixed OFS write operations but unveiled
another bug: files greater than 4KB are being created with a wrong
size resulting in errors like the following:

dd if=/dev/zero of=file bs=4097 count=1
cp file /mnt/affs/
cp: error writing '/mnt/affs/file': Bad address

Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Al Viro <viro@zeniv.linux.org.uk>

fs/affs/file.c

@@ -679,7 +679,7 @@ static int affs_write_end_ofs(struct file *file, struct address_space *mapping,
 	int written;
 
 	from = pos & (PAGE_SIZE - 1);
-	to = pos + len;
+	to = from + len;
 	/*
 	 * XXX: not sure if this can handle short copies (len < copied), but
 	 * we don't have to, because the page should always be uptodate here,