irqchip/riscv-imsic: Inline imsic_vector_from_local_id()

irqchip/riscv-imsic: Inline imsic_vector_from_local_id()

This function is only called from one place, which is in the interrupt
handling hot path. Inline it to improve code generation and to take
advantage of this_cpu operations. lpriv and imsic->base_domain can never be
NULL because irq_set_chained_handler() is called after they are allocated.

Signed-off-by: Samuel Holland <samuel.holland@sifive.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>