ARM: mvebu: Use the a standard errno in mvebu_get_soc_id

Instead of using -1 as error value, use a standard errno.

Signed-off-by: Gregory CLEMENT <gregory.clement@free-electrons.com>
Link: https://lkml.kernel.org/r/1403274953-21790-2-git-send-email-gregory.clement@free-electrons.com


Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Signed-off-by: Jason Cooper <jason@lakedaemon.net>