intel_th: msu: Set fops::owner to prevent module from unloading

Right now it's possible to unload the msu driver while its character
device is open. Prevent it by setting fops::owner, which will result
in the module reference being held while the device node is open.

Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Reviewed-by: Laurent Fert <laurent.fert@intel.com>