spi: hisi-sfc-v3xx: Return IRQ_NONE if no interrupts were detected

Return IRQ_NONE from the interrupt handler when no interrupt was
detected. Because an empty interrupt will cause a null pointer error:

    Unable to handle kernel NULL pointer dereference at virtual
  address 0000000000000008
    Call trace:
        complete+0x54/0x100
        hisi_sfc_v3xx_isr+0x2c/0x40 [spi_hisi_sfc_v3xx]
        __handle_irq_event_percpu+0x64/0x1e0
        handle_irq_event+0x7c/0x1cc

Signed-off-by: Devyn Liu <liudingyuan@huawei.com>
Link: https://msgid.link/r/20240123071149.917678-1-liudingyuan@huawei.com
Signed-off-by: Mark Brown <broonie@kernel.org>