Staging: comedi: Return -EFAULT if copy_to_user() fails

Staging: comedi: Return -EFAULT if copy_to_user() fails

commit cab36da4bf1a35739b091b73714a39a1bbd02b05 upstream.

Return -EFAULT on error instead of the number of bytes remaining to be
copied.

Fixes: bac42fb21259 ("comedi: get rid of compat_alloc_user_space() mess in COMEDI_CMD{,TEST} compat")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Cc: stable <stable@vger.kernel.org>
Link: https://lore.kernel.org/r/X8c3pfwFy2jpy4BP@mwanda
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>