[PATCH] wifi: ath11k: fix warning when unbinding

[Jose Ignacio Tornos Martinez]

Hello Baochen,

As I try to comment in the commit description, the warning is not at
the intialization, but comes up when the device is unbinded after a
problem at the initialization stage, because due to the problem the
buffers were released (probe). Later after the problem, if the unbinding
is commanded the buffers are released again.
Setting to NUll after releasing avoids the double free.

The easiest way to reproduce it is to run in a VM the default upstream
kernel (that is always failing on VMs) and just unbind the device
(ath11k_pci).

The same problem was fixed by me for ath12k driver here ca68ce0d9f4b
("wifi: ath12k: fix warning when unbinding"), and I have seen the same problem
is also happening for ath11k driver.

Thanks

Best regards
José Ignacio