libxl: Use new macro LOGE() in libxl_qmp.c

libxl: Use new macro LOGE() in libxl_qmp.c

Code cleanup -- no functional changes

Coding style has recently been changed for libxl. The convenience
macro LOGE() has been introduced, and invocations of the old macro
LIBXL__LOG_ERROR() are to be replaced with it. Change all occurences
of the old macro (in functions that have a local libxl_gc *gc) except
the one in register_serials_chardev_callback() to the new one. (This
function lacks a local libxl__gc *gc, which LOGE() requires.)

Suggested-by: Anthony PERARD <anthony.perard@citrix.com>
Signed-off-by: Kelley Nielsen <kelleynnn@gmail.com>
Acked-by: Ian Campbell <ian.campbell@citrix.com>