leds: is31fl319x: Cleanup formatting and dev_dbg calls

Fix remaining non-standard place for comments.

Remove remaining dev_dbg after regmap_read in is31fl3196_brightness_set.

Remove __func__ in dev_dbg calls, instead adding "channel" string to
describe the first displayed value.

Change remaining container_of() call to be on one line,
as well as a few others.

Signed-off-by: Vincent Knecht <vincent.knecht@mailoo.org>
Signed-off-by: Pavel Machek <pavel@ucw.cz>