ip2: return -EFAULT on copy_to_user errors

copy_to_user() returns the number of bytes remaining but we want to return
a negative error code on errors.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Cc: "Michael H. Warfield" <mhw@wittsend.com>
Signed-off-by: Andrew Morton <akpm@linux-foundation.org>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>