fbdev: vga16fb: Add missing MODULE_DEVICE_TABLE() entry

This patch adds missing MODULE_DEVICE_TABLE definition
which generates correct modalias for automatic loading
of this driver when it is built as an external module.

Signed-off-by: Zeng Heng <zengheng4@huawei.com>
Signed-off-by: Helge Deller <deller@gmx.de>