replace IS_ERR/PTR_ERR

Cc: Chris Metcalf <cmetcalf@tilera.com>
Cc: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Signed-off-by: Fabian Frederick <fabf@skynet.be>
Signed-off-by: Chris Metcalf <cmetcalf@tilera.com>