gpio/pca953x: Remove dynamic platform data pointer

In the case that we obtain device-tree data to fill in platform_data, the new
platform data struct was dynamically allocated, but the pointer to it was not
used everywhere it should. It seems easier to fix this issue by removing the
dynamic allocation altogether since its data is only used during driver
probing.

Signed-off-by: David Jander <david@protonic.nl>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>