gpio: xilinx: Set value before changing direction

Set a value before changing gpio direction. This will ensure that the
old value is not propagated when direction has changed but new value is
not written yet.

Reported-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>
Signed-off-by: Michal Simek <michal.simek@xilinx.com>
Reviewed-by: Stefan Herbrechtsmeier <stefan@herbrechtsmeier.net>