drm/vc4: Add explicit declaration of 'drmm_of_get_bridge'

Fix the error of implicit declaration of function 'drmm_of_get_bridge':

drivers/gpu/drm/vc4/vc4_dpi.c:278:11: error: implicit declaration of function ‘drmm_of_get_bridge’; did you mean ‘devm_drm_of_get_bridge’? [-Werror=implicit-function-declaration]
  bridge = drmm_of_get_bridge(drm, dev->of_node, 0, 0);

Fixes: 055af023 ("drm/vc4: dpi: Switch to drmm_of_get_bridge")
Signed-off-by: Wang Jingjin <wangjingjin1@huawei.com>
Signed-off-by: Maxime Ripard <maxime@cerno.tech>
Link: https://patchwork.freedesktop.org/patch/msgid/20220716020741.4124893-1-wangjingjin1@huawei.com