fbdev/sm501fb: Output message with fb_err()

Fix case were dev_err() is being called with struct fb_info.dev.
Use fb_err() instead.

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/20230613110953.24176-30-tzimmermann@suse.de