drm/i915/gvt: Add missing breaks in switch statement

drm/i915/gvt: Add missing breaks in switch statement

The switch statement is missing breaks for the cases of
GVT_FAILSAFE_INSUFFICIENT_RESOURCE and GVT_FAILSAFE_GUEST_ERR. Add them
in.

Detected by CoverityScan, CID#1462416 ("Missing break in switch")

Fixes: 635bd44c909d ("drm/i915/gvt: Add VM healthy check for workload_thread")
Fixes: ff9c36967e8e ("drm/i915/gvt: enter failsafe mode when guest requires more resources")
Signed-off-by: Colin Ian King <colin.king@canonical.com>
Signed-off-by: Zhenyu Wang <zhenyuw@linux.intel.com>