KVM: mmu: increase the mmu_notifier_count for legacy APIs

Intel inclusion
category: bugfix
bugzilla: https://gitee.com/openeuler/kernel/issues/I8YDCS


CVE: NA

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Fix kvm_mmu_notifier_invalidate_range_start(), which missed to increase
the mmu_notifier_count. Otherwise BUG_ON() could be triggered later, by
kvm_mmu_notifier_invalidate_range_end(), on platforms using legacy KVM
MMU notifier APIs.

Fixes: ac63cf0a ("KVM: Move MMU notifier's mmu_lock acquisition into common helper")
Reported-by: xianglai li <lixianglai@loongson.cn>
Signed-off-by: Yu Zhang <yu.c.zhang@linux.intel.com>