MAINTAINERS: Fix Hyperv vIOMMU driver file name

The Hyperv vIOMMU file name should be "hyperv-iommu.c" rather
than "hyperv_iommu.c". This patch is to fix it.

Signed-off-by: Lan Tianyu <Tianyu.Lan@microsoft.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>