fbdev/sh7760fb: Output messages with fb_dbg()

Fix cases were output helpers are called with struct fb_info.dev.
Use fb_dbg() instead. 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/20230613110953.24176-27-tzimmermann@suse.de