hw/isa/i82378: Propagate error if PC_SPEAKER device creation failed

hw/isa/i82378: Propagate error if PC_SPEAKER device creation failed

In commit 40f8214fcd ("hw/audio/pcspk: Inline pcspk_init()")
we neglected to give a change to the caller to handle failed
device creation cleanly. Respect the caller API contract and
propagate the error if creating the PC_SPEAKER device ever
failed. This avoid yet another bad API use to be taken as
example and copy / pasted all over the code base.

Reported-by: Bernhard Beschow <shentey@gmail.com>
Suggested-by: Markus Armbruster <armbru@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Bernhard Beschow <shentey@gmail.com>
Signed-off-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Message-Id: <20231020171509.87839-5-philmd@linaro.org>