Fix one dead loop case in host S3

Fix one dead loop case in host S3

Wake sts is only required to be checked for S1, and implementation
is free to not touch wake sts bit for S3. The latter case is observed
falling into loop on checking wake sts after sleep hypercall returns.
Actually we only need to check hypercall return value here, and those
checks belong to Xen instead.

Signed-off-by Kevin Tian <kevin.tian@intel.com>