gpio: pca953x: fix vendor prefix for PCA9654

Despite commit 55020c80 ("of: Add vendor prefix for ON Semiconductor
Corp.") was made long ago, the latter commit 9f49f6dd ("gpio: pca953x:
add onsemi,pca9654 id") made use of another, undocumented vendor prefix.
Since such prefix doesn't seem to be used in any device trees, I think we
can just fix the "compatible" string in the driver and the bindings and be
done with that...

Fixes: 9f49f6dd ("gpio: pca953x: add onsemi,pca9654 id")
Signed-off-by: Sergei Shtylyov <sergei.shtylyov@cogentembedded.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Linus Walleij <linus.walleij@linaro.org>