drm/hisilicon: Fix build error

Fix the following errors:
divers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c:
In function ‘hibmc_hw_map’:
drivers/gpu/drm/hisilicon/hibmc/hibmc_drm_drv.c:213:25:
error: ‘dev’ undeclared (first use in this function);

Fixes: 4d4dad21 ("drm/hibmc: Remove references to struct drm_device.pdev")
Signed-off-by: Tian Tao <tiantao6@hisilicon.com>
Acked-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/1610529568-25754-1-git-send-email-tiantao6@hisilicon.com