intel_th: msu: Release resources on read error

Right now, reading from msc character device will leak its's user count
on read error.

This patch makes sure resources are released when there is no data left
to read from the buffer.

Signed-off-by: Laurent FERT <laurent.fert@intel.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>