drm: bridge: adv7511: unregister cec i2c device after cec adapter

In the Linux kernel, the following vulnerability has been resolved:

drm: bridge: adv7511: unregister cec i2c device after cec adapter

cec_unregister_adapter() assumes that the underlying adapter ops are
callable. For example, if the CEC adapter currently has a valid physical
address, then the unregistration procedure will invalidate the physical
address by setting it to f.f.f.f. Whence the following kernel oops
observed after removing the adv7511 module:

Unable to handle kernel execution of user memory at virtual address 0000000000000000
Internal error: Oops: 86000004 [#1] PREEMPT_RT SMP
Call trace:
0x0
adv7511_cec_adap_log_addr+0x1ac/0x1c8 [adv7511]
cec_adap_unconfigure+0x44/0x90 [cec]
__cec_s_phys_addr.part.0+0x68/0x230 [cec]
__cec_s_phys_addr+0x40/0x50 [cec]
cec_unregister_adapter+0xb4/0x118 [cec]
adv7511_remove+0x60/0x90 [adv7511]
i2c_device_remove+0x34/0xe0
device_release_driver_internal+0x114/0x1f0
driver_detach+0x54/0xe0
bus_remove_driver+0x60/0xd8
driver_unregister+0x34/0x60
i2c_del_driver+0x2c/0x68
adv7511_exit+0x1c/0x67c [adv7511]
__arm64_sys_delete_module+0x154/0x288
invoke_syscall+0x48/0x100
el0_svc_common.constprop.0+0x48/0xe8
do_el0_svc+0x28/0x88
el0_svc+0x1c/0x50
el0t_64_sync_handler+0xa8/0xb0
el0t_64_sync+0x15c/0x160
Code: bad PC value
---[ end trace 0000000000000000 ]---

Protect against this scenario by unregistering i2c_cec after
unregistering the CEC adapter. Duly disable the CEC clock afterwards
too.