drm/hisilicon: Remove unused delarations

hibmc_mm_init() has been removed since commit 28645ae0
("drm/hisilicon/hibmc: Remove hibmc_ttm.c"), but remain the declaration
untouched in the header files. So, let's remove this unused declaration.
Signed-off-by: Zhang Zekun <zhangzekun11@huawei.com>
Reviewed-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20240812123543.64300-1-zhangzekun11@huawei.com

drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.h

@@ -57,7 +57,6 @@ void hibmc_set_current_gate(struct hibmc_drm_private *priv,
 int hibmc_de_init(struct hibmc_drm_private *priv);
 int hibmc_vdac_init(struct hibmc_drm_private *priv);
 
-int hibmc_mm_init(struct hibmc_drm_private *hibmc);
 int hibmc_ddc_create(struct drm_device *drm_dev, struct hibmc_connector *connector);
 
 #endif