KVM: arm64: Use find_vma_intersection()

find_vma_intersection() has been existing to search the intersected
vma. This uses the function where it's applicable, to simplify the
code.

Signed-off-by: Gavin Shan <gshan@redhat.com>
Reviewed-by: Keqian Zhu <zhukeqian1@huawei.com>
Signed-off-by: Marc Zyngier <maz@kernel.org>
Link: https://lore.kernel.org/r/20210316041126.81860-3-gshan@redhat.com