media: rkisp1: isp: Rename rkisp1_get_remote_source()

Rename the rkisp1_get_remote_source() function to
rkisp1_isp_get_source() to use a consistent rkisp1_isp_* prefix for all
ISP functions, and drop the "remote" as the source can't be local.

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>