Moved IRQ registration down to end of adv7511_probe().

If an IRQ already is pending during adv7511_probe
(before adv7511_cec_init) then cec_received_msg_ts
could crash using uninitialized data:

    Unable to handle kernel read from unreadable memory at virtual address 00000000000003d5
    Internal error: Oops: 96000004 [#1] PREEMPT_RT SMP
    Call trace:
     cec_received_msg_ts+0x48/0x990 [cec]
     adv7511_cec_irq_process+0x1cc/0x308 [adv7511]
     adv7511_irq_process+0xd8/0x120 [adv7511]
     adv7511_irq_handler+0x1c/0x30 [adv7511]
     irq_thread_fn+0x30/0xa0
     irq_thread+0x14c/0x238
     kthread+0x190/0x1a8

Fixes: 3b1b9750 ("drm: adv7511/33: add HDMI CEC support")
Signed-off-by: Mads Bligaard Nielsen <bli@bang-olufsen.dk>
Signed-off-by: Alvin Šipraga <alsi@bang-olufsen.dk>
Reviewed-by: Robert Foss <rfoss@kernel.org>
Signed-off-by: Robert Foss <rfoss@kernel.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20240219-adv7511-cec-irq-crash-fix-v2-1-245e53c4b96f@bang-olufsen.dk