stubdom/xenstored: Fix uninitialised variables in lu_read_state()

stubdom/xenstored: Fix uninitialised variables in lu_read_state()

Various version of gcc, when compiling with -Og, complain:

  xenstored_control.c: In function ‘lu_read_state’:
  xenstored_control.c:540:11: error: ‘state.size’ is used uninitialized in this
  function [-Werror=uninitialized]
    if (state.size == 0)
        ~~~~~^~~~~
  xenstored_control.c:543:6: error: ‘state.buf’ may be used uninitialized in
  this function [-Werror=maybe-uninitialized]
    pre = state.buf;
    ~~~~^~~~~~~~~~~
  xenstored_control.c:550:23: error: ‘state.buf’ may be used uninitialized in
  this function [-Werror=maybe-uninitialized]
     (void *)head - state.buf < state.size;
                    ~~~~~^~~~
  xenstored_control.c:550:35: error: ‘state.size’ may be used uninitialized in
  this function [-Werror=maybe-uninitialized]
     (void *)head - state.buf < state.size;
                                ~~~~~^~~~~

for the stubdom build.  This is because lu_get_dump_state() is a no-op stub in
MiniOS, and state really is operated on uninitialised.

Signed-off-by: Andrew Cooper <andrew.cooper3@citrix.com>
Reviewed-by: Juergen Gross <jgross@suse.com>
Reviewed-by: Ian Jackson <iwj@xenproject.org>
Release-Acked-by: Ian Jackson <iwj@xenproject.org>