drm/i915/gvt: cleanup some too chatty scheduler message

It's too chatty to have three places to tell us which one
is next vgpu for schedule. My log file was bloated to eat
all disk space..

Cc: Ping Gao <ping.a.gao@intel.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>