clk: imx: rename video_pll1 to video_pll

Unlike audio_pll1 and audio_pll2, there is no video_pll2. Further, the
name used in the RM is video_pll. So, let's rename "video_pll1" to
"video_pll" to be consistent with the RM and avoid misunderstandings.

The IMX8MN_VIDEO_PLL1* constants have not been removed to ensure
backward compatibility of the patch.

No functional changes intended.

Fixes: 96d6392b ("clk: imx: Add support for i.MX8MN clock driver")
Signed-off-by: Dario Binacchi <dario.binacchi@amarulasolutions.com>
Acked-by: Marco Felsch <m.felsch@pengutronix.de>
Reviewed-by: Abel Vesa <abel.vesa@linaro.org>
Signed-off-by: Abel Vesa <abel.vesa@linaro.org>
Link: https://lore.kernel.org/r/20221117113637.1978703-4-dario.binacchi@amarulasolutions.com