sticon: make sticon_set_def_font() void and remove op parameter

sticon_set_def_font() always returns 0, so make it void. And remove an
unused 'op' parameter.

Signed-off-by: "Jiri Slaby (SUSE)" <jirislaby@kernel.org>
Cc: "James E.J. Bottomley" <James.Bottomley@HansenPartnership.com>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-parisc@vger.kernel.org
Cc: linux-fbdev@vger.kernel.org
Cc: dri-devel@lists.freedesktop.org
Signed-off-by: Helge Deller <deller@gmx.de>