iommu/vt-d: Remove an unused variable "length"

The linux-next commit "iommu/vt-d: Duplicate iommu_resv_region objects
per device list" [1] left out an unused variable,

drivers/iommu/intel-iommu.c: In function 'dmar_parse_one_rmrr':
drivers/iommu/intel-iommu.c:4014:9: warning: variable 'length' set but
not used [-Wunused-but-set-variable]

[1] https://lore.kernel.org/patchwork/patch/1083073/



Signed-off-by: Qian Cai <cai@lca.pw>
Reviewed-by: Eric Auger <eric.auger@redhat.com>
Signed-off-by: Joerg Roedel <jroedel@suse.de>