fbdev/sh7760fb: Use fb_dbg() in sh7760fb_get_color_info()

Give struct fb_info to sh7760fb_get_color_info() and use it in
call to fb_dbg(). Prepares fbdev for making struct fb_info.dev
optional.

Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
Reviewed-by: Sam Ravnborg <sam@ravnborg.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613110953.24176-26-tzimmermann@suse.de