drm/rockchip: vop2: Drop unused if_dclk_rate variable

Commit 5a028e8 ("drm/rockchip: vop2: Add support for rk3588")
introduced a variable which ended up being unused:

rockchip_drm_vop2.c:1688:23: warning: variable ‘if_dclk_rate’ set but not used [-Wunused-but-set-variable]

This has been initially used as part of a formula to compute the clock
dividers, but eventually it has been replaced by static values.

Drop the variable declaration and move its assignment to the comment
block, to serve as documentation of how the constants have been
generated.

Signed-off-by: Cristian Ciocaltea <cristian.ciocaltea@collabora.com>
Signed-off-by: Heiko Stuebner <heiko@sntech.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240105174007.98054-1-cristian.ciocaltea@collabora.com

Author: cristicc

drivers/gpu/drm/rockchip/rockchip_drm_vop2.c

@@ -1680,7 +1680,6 @@ static unsigned long rk3588_calc_cru_cfg(struct vop2_video_port *vp, int id,
 	unsigned long dclk_core_rate = v_pixclk >> 2;
 	unsigned long dclk_rate = v_pixclk;
 	unsigned long dclk_out_rate;
-	unsigned long if_dclk_rate;
 	unsigned long if_pixclk_rate;
 	int K = 1;
 
@@ -1695,8 +1694,8 @@ static unsigned long rk3588_calc_cru_cfg(struct vop2_video_port *vp, int id,
 		}
 
 		if_pixclk_rate = (dclk_core_rate << 1) / K;
-		if_dclk_rate = dclk_core_rate / K;
 		/*
+		 * if_dclk_rate = dclk_core_rate / K;
 		 * *if_pixclk_div = dclk_rate / if_pixclk_rate;
 		 * *if_dclk_div = dclk_rate / if_dclk_rate;
 		 */