net: bcmgenet: abort suspend on error

If an error occurs during suspension of the driver the driver should
restore the hardware configuration and return an error to force the
system to resume.

Fixes: 0db55093 ("net: bcmgenet: return correct value 'ret' from bcmgenet_power_down")
Signed-off-by: Doug Berger <opendmb@gmail.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>