fbdev: s1d13xxxfb: add missed unregister_framebuffer in remove

The driver calls register_framebuffer() in probe but does not call
unregister_framebuffer() in remove.
Rename current remove to __s1d13xxxfb_remove() for error handler.
Then add a new remove to call unregister_framebuffer().

Signed-off-by: Chuhong Yuan <hslester96@gmail.com>
Cc: Kristoffer Ericson <kristoffer.ericson@gmail.com>
[b.zolnierkie: ported over recent s1d13xxxfb changes]
[b.zolnierkie: removed extra newline]
Signed-off-by: Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200324132311.21729-1-hslester96@gmail.com