fbdev: matrox: use modern module_init()

This is one of the last drivers with a global init_module() function
instead of the modern module_init() annotation. Convert it over.

Signed-off-by: Arnd Bergmann <arnd@arndb.de>
Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Link: https://patchwork.freedesktop.org/patch/msgid/20210514213316.635070-1-arnd@kernel.org