qeth: use qeth_card_hw_is_reachable() everywhere

qeth_card_hw_is_reachable() was introduced as part of a new
functionality, but it is a useful abstraction that can replace
verbose checks througout the rest of the `qeth` driver.

Signed-off-by: Eugene Crosser <Eugene.Crosser@ru.ibm.com>
Signed-off-by: Ursula Braun <ursula.braun@de.ibm.com>
Reviewed-by: Thomas-Mich Richter <tmricht@de.ibm.com>
Signed-off-by: David S. Miller <davem@davemloft.net>