leds: pca963x: cosmetic: use helper variables, better indentation

Use helper variables: instead of writing &client->dev at many places,
write only dev. The same with pca963x->chip->chipdef,
pca963x->chip->client).

Use helper variable u8 val for i2c_smbus_write_byte_data, for better
indentation.

Indent better on various places.
Signed-off-by: Marek Behún <marek.behun@nic.cz>
Cc: Peter Meerwald <p.meerwald@bct-electronic.com>
Cc: Ricardo Ribalda <ribalda@kernel.org>
Cc: Zahari Petkov <zahari@balena.io>
Signed-off-by: Pavel Machek <pavel@ucw.cz>