riscv: Fix NR_CPUS range conditions

The conditions reference the symbol SBI_V01, which does not exist. The
correct symbol is RISCV_SBI_V01.

Fixes: e623715f

 ("RISC-V: Increase range and default value of NR_CPUS")
Signed-off-by: Samuel Holland <samuel@sholland.org>
Reviewed-by: Andrew Jones <ajones@ventanamicro.com>
Reviewed-by: Conor Dooley <conor.dooley@microchip.com>
Link: https://lore.kernel.org/r/20221126061557.3541-1-samuel@sholland.org
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>