soc: apple: mailbox: fix device leak on lookup

soc: apple: mailbox: fix device leak on lookup

Make sure to drop the reference taken to the mbox platform device when
looking up its driver data.

Note that holding a reference to a device does not prevent its driver
data from going away so there is no point in keeping the reference.

Fixes: 6e1457fcad3f ("soc: apple: mailbox: Add ASC/M3 mailbox driver")
Cc: stable@vger.kernel.org	# 6.8
Signed-off-by: Johan Hovold <johan@kernel.org>
Reviewed-by: Neal Gompa <neal@gompa.dev>
Signed-off-by: Sven Peter <sven@kernel.org>