hw/nmi: Remove unused @errp argument from raise_nmi()

Not a single handler update @errp. The single user is
nmi_inject() filling with "machine does not provide NMIs".
Remove the unused argument from the raise_nmi() callback,
simplifying the methods in hw/core/nmi.c.

Signed-off-by: Philippe Mathieu-Daudé <philmd@oss.qualcomm.com>
Reviewed-by: Marc-André Lureau <marcandre.lureau@redhat.com>
Message-Id: <20260812121232.71958-7-philmd@oss.qualcomm.com>