lib: sbi_hsm: Optimize sbi_hsm_hart_get_state() implementation

Now that sbi_hart_id_to_scratch() is optimized, we don't need
the "if ()" statement. Also, the hstate local variable is
redundant so we remove that as well.

Signed-off-by: Anup Patel <anup.patel@wdc.com>
Reviewed-by: Atish Patra <atish.patra@wdc.com>