drm/i915: check for -EINVAL from vm_insert_pfn

Indicates something is wrong with the mapping; and apparently triggers
in current kernels.

Signed-off-by: Jesse Barnes <jbarnes@virtuosugeek.org>
Signed-off-by: Eric Anholt <eric@anholt.net>

drivers/gpu/drm/i915/i915_gem.c

@@ -1072,6 +1072,7 @@ int i915_gem_fault(struct vm_area_struct *vma, struct vm_fault *vmf)
 	case -EAGAIN:
 		return VM_FAULT_OOM;
 	case -EFAULT:
+	case -EINVAL:
 		return VM_FAULT_SIGBUS;
 	default:
 		return VM_FAULT_NOPAGE;