mshv: Only map vp->vp_stats_pages if on root scheduler

This mapping is only used for checking if the dispatch thread is
blocked. This is only relevant for the root scheduler, so check the
scheduler type to determine whether to map/unmap these pages, instead of
the current check, which is incorrect.

Signed-off-by: Nuno Das Neves <nunodasneves@linux.microsoft.com>
Reviewed-by: Anirudh Rayabharam <anirudh@anirudhrb.com>
Reviewed-by: Praveen K Paladugu <prapal@linux.microsoft.com>
Reviewed-by: Easwar Hariharan <easwar.hariharan@linux.microsoft.com>
Reviewed-by: Tianyu Lan <tiala@microsoft.com>
Acked-by: Stanislav Kinsburskii <skinsburskii@linux.microsoft.com>
Reviewed-by: Anirudh Rayabharam (Microsoft) <anirudh@anirudhrb.com>
Signed-off-by: Wei Liu <wei.liu@kernel.org>