net: dsa: sja1105: don't keep a persistent reference to the reset GPIO

The driver only needs the reset GPIO for a very brief period, so instead
of using devres and keeping the descriptor pointer inside priv, just use
that descriptor inside the sja1105_hw_reset function and then let go of
it.

Also use gpiod_get_optional while at it, and error out on real errors
(bad flags etc).

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
Signed-off-by: David S. Miller <davem@davemloft.net>