bnx2: don't request firmware when there's no userspace.

bnx2: don't request firmware when there's no userspace.

The firmware is cached during the first successful call to open() and
released once the network device is unregistered. The driver uses the
cached firmware between open() and unregister_netdev().

It's similar to 953a12cc2889d1be92e80a2d0bab5ffef4942300 but the
firmware is mandatory.

(cherry picked from commit 7880b72e94fd3cf3283de6752175191583bce9f0)
Signed-off-by: Francois Romieu <romieu@fr.zoreil.com>
Reviewed-by: Michael Chan <mchan@broadcom.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
Signed-off-by: Joe Jin <joe.jin@oracle.com>