fbdev: Fix cfb_imageblit() for arbitrary image widths

Commit 0d030118

 ("fbdev: Improve performance of cfb_imageblit()")
broke cfb_imageblit() for image widths that are not aligned to 8-bit
boundaries. Fix this by handling the trailing pixels on each line
separately. The performance improvements in the original commit do not
regress by this change.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Fixes: 0d030118

 ("fbdev: Improve performance of cfb_imageblit()")
Reported-by: Marek Szyprowski <m.szyprowski@samsung.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Sam Ravnborg <sam@ravnborg.org>
Tested-by: Marek Szyprowski <m.szyprowski@samsung.com>
Acked-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Tested-by: Guenter Roeck <linux@roeck-us.net>
Signed-off-by: Dave Airlie <airlied@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20220313192952.12058-3-tzimmermann@suse.de