agp/intel: Fix a memory leak on module initialisation failure

In intel_gtt_setup_scratch_page(), pointer "page" is not released if
pci_dma_mapping_error() return an error, leading to a memory leak on
module initialisation failure.  Simply fix this issue by freeing "page"
before return.

Fixes: 0e87d2b06c ("intel-gtt: initialize our own scratch page")
Signed-off-by: Qiushi Wu <wu000273@umn.edu>
Reviewed-by: Chris Wilson <chris@chris-wilson.co.uk>
Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Link: https://patchwork.freedesktop.org/patch/msgid/20200522083451.7448-1-chris@chris-wilson.co.uk

drivers/char/agp/intel-gtt.c

@@ -304,8 +304,10 @@ static int intel_gtt_setup_scratch_page(void)
 	if (intel_private.needs_dmar) {
 		dma_addr = pci_map_page(intel_private.pcidev, page, 0,
 				    PAGE_SIZE, PCI_DMA_BIDIRECTIONAL);
-		if (pci_dma_mapping_error(intel_private.pcidev, dma_addr))
+		if (pci_dma_mapping_error(intel_private.pcidev, dma_addr)) {
+			__free_page(page);
 			return -EINVAL;
+		}
 
 		intel_private.scratch_page_dma = dma_addr;
 	} else