The copy_to_user() function returns the number of bytes remaining but
we want to return -EFAULT to the user if it can't complete the copy.
The "st" variable only holds zero on success or negative error codes on
failure so the type should be int.

Fixes: 36f988e9 ("rsxx: Adding in debugfs entries.")
Signed-off-by: NDan Carpenter <dan.carpenter@oracle.com>
Signed-off-by: NJens Axboe <axboe@kernel.dk>