accel: abort if we fail to load the accelerator plugin

accel: abort if we fail to load the accelerator plugin

if QEMU is configured with modules enabled, it is possible that the
load of an accelerator module will fail.
Exit in this case, relying on module_object_class_by_name to report
the specific load error if any.

Signed-off-by: Claudio Fontana <cfontana@suse.de>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
[claudio: changed abort() to exit(1)]
Reviewed-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20220929093035.4231-6-cfontana@suse.de>

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>