fbcon: Declare struct fb_info.fbcon_par as of type struct fbcon_par

The only correct type for the field fbcon_par in struct fb_info
is struct fbcon_par. Declare is as such. The field is a pointer
to fbcon-private data.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Signed-off-by: Helge Deller <deller@gmx.de>