drm: Remove unused function rcar_cmm_write

The function are defined in the rcar_cmm.c file, but not called
elsewhere, so delete the unused function.

drivers/gpu/drm/renesas/rcar-du/rcar_cmm.c:35:19: warning: unused function 'rcar_cmm_read'.

Reported-by: Abaci Robot <[e-mail]>
Closes: https://bugzilla.openanolis.cn/show_bug.cgi?id=9364
Signed-off-by: Jiapeng Chong <[e-mail]>
Reviewed-by: Kieran Bingham <[e-mail]>
Reviewed-by: Laurent Pinchart <[e-mail]>
Link: https://lore.kernel.org/r/[e-mail]
Signed-off-by: Tomi Valkeinen <[e-mail]>

drivers/gpu/drm/renesas/rcar-du/rcar_cmm.c

···
 	} lut;
 };
 
-static inline int rcar_cmm_read(struct rcar_cmm *rcmm, u32 reg)
-{
-	return ioread32(rcmm->base + reg);
-}
-
 static inline void rcar_cmm_write(struct rcar_cmm *rcmm, u32 reg, u32 data)
 {
 	iowrite32(data, rcmm->base + reg);