fbdev/acornfb: Fix name of fb_ops initializer macro

Fix build by using the correct name for the initializer macro
for struct fb_ops.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 9037afde

 ("fbdev/acornfb: Use fbdev I/O helpers")
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Sam Ravnborg <sam@ravnborg.org>
Cc: Helge Deller <deller@gmx.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Arnd Bergmann <arnd@arndb.de>
Cc: <stable@vger.kernel.org> # v6.6+
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20231127131655.4020-2-tzimmermann@suse.de