atmel: return ENOENT on request_firmware failure

Return errors from request_firmware() (like other drivers that do
firmware load on device open) and make up plausible codes for other
error conditions. Gives userspace tools like NetworkManager a clue that
firmware may be missing when the result of setting IFF_UP is ENOENT.

Signed-off-by: Dan Williams <dcbw@redhat.com>
v2: fix reversed check of atmel_wakeup_firmware() in probe_atmel_card()
Signed-off-by: John W. Linville <linville@tuxdriver.com>