dt-bindings: leds: fix macro names for pca955x

The documentation reports the wrong macro names
related to the pca9532 instead of the pca955x

Signed-off-by: Flavio Suligoi <f.suligoi@asem.it>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>