drm/gma500: Add fb gtt offset to fb base

Old code assumed framebuffer starts at base of stolen memory. Since the
addition of hardware cursors, this might not be true anymore so add the
gtt offset to the calculation.
Reported-by: Holger Schurig <holgerschurig@gmail.com>
Tested-by: Holger Schurig <holgerschurig@gmail.com>
Signed-off-by: Patrik Jakobsson <patrik.r.jakobsson@gmail.com>

drivers/gpu/drm/gma500/framebuffer.c

@@ -121,8 +121,8 @@ static int psbfb_vm_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	unsigned long address;
 	int ret;
 	unsigned long pfn;
-	/* FIXME: assumes fb at stolen base which may not be true */
-	unsigned long phys_addr = (unsigned long)dev_priv->stolen_base;
+	unsigned long phys_addr = (unsigned long)dev_priv->stolen_base +
+				  psbfb->gtt->offset;
 
 	page_num = (vma->vm_end - vma->vm_start) >> PAGE_SHIFT;
 	address = (unsigned long)vmf->virtual_address - (vmf->pgoff << PAGE_SHIFT);