drm/i915/kvmgt: Fix compilation error

gvt_pin_guest_page extracted some of the gvt_dma_map_page functionality:
commit 79e542f5 ("drm/i915/kvmgt: Support setting dma map for huge pages")

And yet, part of it was reintroduced in:
commit 39b4cbad ("drm/i915/kvmgt: Check the pfn got from vfio_pin_pages")

Causing kvmgt part to no longer build. Let's remove it.
Reported-by: Tomasz Lis <tomasz.lis@intel.com>
Signed-off-by: Michał Winiarski <michal.winiarski@intel.com>
Cc: Changbin Du <changbin.du@intel.com>
Cc: Zhenyu Wang <zhenyuw@linux.intel.com>
Acked-by: Zhenyu Wang <zhenyuw@linux.intel.com>
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20180712155330.32055-1-michal.winiarski@intel.com
(cherry picked from commit 4eaf317a)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/gvt/kvmgt.c

@@ -185,12 +185,6 @@ static int gvt_dma_map_page(struct intel_vgpu *vgpu, unsigned long gfn,
 	if (ret)
 		return ret;
 
-	if (!pfn_valid(pfn)) {
-		gvt_vgpu_err("pfn 0x%lx is not mem backed\n", pfn);
-		vfio_unpin_pages(mdev_dev(vgpu->vdev.mdev), &gfn, 1);
-		return -EINVAL;
-	}
-
 	/* Setup DMA mapping. */
 	*dma_addr = dma_map_page(dev, page, 0, size, PCI_DMA_BIDIRECTIONAL);
 	ret = dma_mapping_error(dev, *dma_addr);