riscv: spinwait: Fix hartid variable type

The hartid variable is of type int but compared with
ULONG_MAX(INVALID_HARTID). This issue is fixed by changing
the hartid variable type to unsigned long.

Fixes: c78f94f3

 ("RISC-V: Use __cpu_up_stack/task_pointer only for spinwait method")

Signed-off-by: Sunil V L <sunilvl@ventanamicro.com>
Reviewed-by: Atish Patra <atishp@rivosinc.com>
Link: https://lore.kernel.org/r/20220527051743.2829940-3-sunilvl@ventanamicro.com
Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>