gpio: pca953x: remove unneeded check for chip type

We can assume our own device_id table is correct, so remove checking if
the chip type is valid. (The check was bogus anyway: If it found an
invalid entry, it returned with 0!) This is in preparation for further
cleanups.

Signed-off-by: Wolfram Sang <w.sang@pengutronix.de>
Cc: Grant Likely <grant.likely@secretlab.ca>
Signed-off-by: Grant Likely <grant.likely@secretlab.ca>