hw/riscv: Fix typo field in error_report

hw/riscv: Fix typo field in error_report

"smp.cpus" means the number of online CPUs and "smp.max_cpus" means the
total number of CPUs.

riscv_numa_get_default_cpu_node_id() checks "smp.cpus" and the
"available CPUs" description in the next error message also indicates
online CPUs.

So report "smp.cpus" in error_report() instand of "smp.max_cpus".

Since "smp.cpus" is "unsigned int", use "%u".

Signed-off-by: Zhao Liu <zhao1.liu@intel.com>
Reviewed-by: Alistair Francis <alistair.francis@wdc.com>
Message-Id: <20230718080712.503333-1-zhao1.liu@linux.intel.com>
Signed-off-by: Alistair Francis <alistair.francis@wdc.com>