media: dt-bindings: media: rkisp1: fix pclk clock-name

Having a clock name as "pclk_isp" suggests really hard a remnant from
the vendor kernel.

Right now no driver _and_ no devicetree actually uses this clock name
so there is still time to fix that naming.

Therefore drop the "_isp" suffix and only name it pclk.

Signed-off-by: Heiko Stuebner <heiko.stuebner@theobroma-systems.com>
Acked-by: Rob Herring <robh@kernel.org>
Signed-off-by: Hans Verkuil <hverkuil-cisco@xs4all.nl>
Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>