qemu-options: Tweak [, maxcpus=cpus] to [, maxcpus=maxcpus]

qemu-options: Tweak [, maxcpus=cpus] to [, maxcpus=maxcpus]

In qemu-option.hx, there is "-smp [[cpus=]n][,maxcpus=cpus]..." in the
DEF part, and "-smp [[cpus=]n][,maxcpus=maxcpus]..." in the RST part.
Obviously the later is right, let's fix the previous one.

Signed-off-by: Yanan Wang <wangyanan55@huawei.com>
Reviewed-by: Damien Hedde <damien.hedde@greensocs.com>
Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Message-Id: <20210928121134.21064-2-wangyanan55@huawei.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>