fbdev/mb862xxfb: Output messages with fb_dbg()

Fix cases were output helpers are called with struct fb_info.dev.
Use fb_dbg() instead. Prepares fbdev for making struct fb_info.dev
optional.

v2:
	* fix another reference to struct fb_info.dev (kernel test reobot)
	* remove fb_err() from commit message

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-17-tzimmermann@suse.de