riscv: Use LIST_HEAD() to simplify code

list_head can be initialized automatically with LIST_HEAD()
instead of calling INIT_LIST_HEAD().

Signed-off-by: Jinjie Ruan <ruanjinjie@huawei.com>
Tested-by: Charlie Jenkins <charlie@rivosinc.com>
Reviewed-by: Charlie Jenkins <charlie@rivosinc.com>
Link: https://lore.kernel.org/r/20240904013344.2026738-1-ruanjinjie@huawei.com


Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>