ENODATA doesn't exist on FreeBSD, so ENODATA errors returned by the
hypervisor are translated to ENOENT.

Also, the error code is returned in errno if the call returns -1, so
compare the error code with the value in errno instead of the value
returned by the function.

Signed-off-by: Roger Pau Monné <roger.pau@citrix.com>
Signed-off-by: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: xen-devel@lists.xenproject.org
Cc: Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Cc: Anthony Perard <anthony.perard@citrix.com>