wcn36xx: Close SMD channel on device removal

The SMD channel is not the primary WCNSS channel and must explicitly be
closed as the device is removed, or the channel will already by open on
a subsequent probe call in e.g. the case of reloading the kernel module.

This issue was introduced because I simplified the underlying SMD
implementation while the SMD adaptions of the driver sat on the mailing
list, but missed to update these patches. The patch does however only
apply back to the transition to rpmsg, hence the limited Fixes.

Fixes: 5052de8d ("soc: qcom: smd: Transition client drivers from smd to rpmsg")
Reported-by: Eyal Ilsar <c_eilsar@qti.qualcomm.com>
Signed-off-by: Bjorn Andersson <bjorn.andersson@linaro.org>