irqchip/riscv-imsic: Start local sync timer on correct CPU

When starting the local sync timer to synchronize the state of a remote
CPU it should be added on the CPU to be synchronized, not the initiating
CPU. This results in interrupt delivery being delayed until the timer
eventually runs (due to another mask/unmask/migrate operation) on the
target CPU.

Fixes: 0f67911e ("irqchip/riscv-imsic: Separate next and previous pointers in IMSIC vector")
Signed-off-by: Andrew Bresticker <abrestic@rivosinc.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Reviewed-by: Anup Patel <anup@brainfault.org>
Link: https://lore.kernel.org/all/20250514171320.3494917-1-abrestic@rivosinc.com