media: rkisp1: Clean up LSC configuration code

Clean up the LSC configuration code to improve its readability by
shortening lines, using extra local variables and renaming long
variables. No functional change intended.

Signed-off-by: Laurent Pinchart <laurent.pinchart@ideasonboard.com>
Reviewed-by: Dafna Hirschfeld <dafna@fastmail.com>
Signed-off-by: Mauro Carvalho Chehab <mchehab@kernel.org>