drm/ssd130x: Fix include guard name

This is a leftover from an early iteration of the driver when it was still
named ssd1307 instead of ssd130x. Change it for consistency with the rest.

Signed-off-by: Javier Martinez Canillas <javierm@redhat.com>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Reviewed-by: Sui Jingfeng <suijingfeng@loongson.cn>
Link: https://patchwork.freedesktop.org/patch/msgid/20230512120232.304603-1-javierm@redhat.com