net: wwan: iosm: fix NULL pointer dereference when removing device

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

net: wwan: iosm: fix NULL pointer dereference when removing device

In suspend and resume cycle, the removal and rescan of device ends

up in NULL pointer dereference.

During driver initialization, if the ipc_imem_wwan_channel_init()

fails to get the valid device capabilities it returns an error and

further no resource (wwan struct) will be allocated. Now in this

situation if driver removal procedure is initiated it would result

in NULL pointer exception since unallocated wwan struct is dereferenced

inside ipc_wwan_deinit().

ipc_imem_run_state_worker() to handle the called functions return value

and to release the resource in failure case. It also reports the link

down event in failure cases. The user space application can handle this

event to do a device reset for restoring the device communication.