stm class: Fix a double free of stm_source_device

commit 961b6ffe

 upstream.

In the error path of stm_source_register_device(), the kfree is
unnecessary, as the put_device() before it ends up calling
stm_source_device_release() to free stm_source_device, leading to
a double free at the outer kfree() call. Remove it.

Signed-off-by: Ding Xiang <dingxiang@cmss.chinamobile.com>
Signed-off-by: Alexander Shishkin <alexander.shishkin@linux.intel.com>
Fixes: 7bd1d409

 ("stm class: Introduce an abstraction for System Trace Module devices")
Link: https://lore.kernel.org/linux-arm-kernel/1563354988-23826-1-git-send-email-dingxiang@cmss.chinamobile.com/
Cc: stable@vger.kernel.org # v4.4+
Link: https://lore.kernel.org/r/20190821074955.3925-2-alexander.shishkin@linux.intel.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>