drm/fbdev-generic: Rename struct fb_info 'fbi' to 'info'

The generic fbdev emulation names variables of type struct fb_info
both 'fbi' and 'info'. The latter seems to be more common in fbdev
code, so name fbi accordingly.

Also replace the duplicate variable in drm_fbdev_fb_destroy().

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20230125200415.14123-11-tzimmermann@suse.de