fbcon: Export fbcon_update_vcs

fbcon: Export fbcon_update_vcs

I failed to spot this while compile-testing. Oops.

Reported-by: kbuild test robot <lkp@intel.com>
Fixes: 9e1467002630 ("fbcon: replace FB_EVENT_MODE_CHANGE/_ALL with direct calls")
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Cc: Daniel Thompson <daniel.thompson@linaro.org>
Cc: Lee Jones <lee.jones@linaro.org>
Cc: Jingoo Han <jingoohan1@gmail.com>
Cc: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc: Daniel Vetter <daniel.vetter@ffwll.ch>
Cc: Hans de Goede <hdegoede@redhat.com>
Cc: Yisheng Xie <ysxie@foxmail.com>
Cc: "Michał Mirosław" <mirq-linux@rere.qmqm.pl>
Cc: Peter Rosin <peda@axentia.se>
Cc: Mikulas Patocka <mpatocka@redhat.com>
Cc: linux-fbdev@vger.kernel.org
Cc: Gerd Hoffmann <kraxel@redhat.com>
Cc: Geert Uytterhoeven <geert+renesas@glider.be>
Cc: Lukas Wunner <lukas@wunner.de>
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20190619081115.27921-1-daniel.vetter@ffwll.ch