USB: at91: at91-ohci: fix set/get power

in commit aa6e52a3

 we introduce the support of overcurrent notification
but the set and get of the power without checking if the gpio is valid or not

Signed-off-by: Jean-Christophe PLAGNIOL-VILLARD <plagnioj@jcrosoft.com>
Acked-by: Thomas Petazzoni <thomas.petazzoni@free-electrons.com>
Acked-by: Nicolas Ferre <nicolas.ferre@atmel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@suse.de>