isdn/kcapi: return -EFAULT on copy_from_user errors

copy_from_user() returns the number of bytes remaining but we should
return -EFAULT here.  The error code gets returned to the user.  Both
old_capi_manufacturer() and capi20_manufacturer() had other places
that already returned -EFAULT so this won't break anything.

Signed-off-by: Dan Carpenter <error27@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>