Utils: Initialize DeviceShell member on ctor

It is initialized in start(), which is called in the worker thread.

Reported by Coverity.

Change-Id: I385b185c220f5be20cc312eb960658c2de770a9c
Reviewed-by: hjk <hjk@qt.io>
Reviewed-by: Marcus Tillmanns <marcus.tillmanns@qt.io>

src/libs/utils/deviceshell.h

@@ -74,7 +74,7 @@ private:
     void closeShellProcess();
 
 private:
-    QtcProcess *m_shellProcess;
+    QtcProcess *m_shellProcess = nullptr;
     QThread m_thread;
 };