drm/i915: Change i915_vma_unbind() to report -EAGAIN on activity

If someone else acquires the i915_vma before we complete our wait and
unbind it, we currently error out with -EBUSY. Use -EAGAIN instead so
that if necessary the caller is prepared to try again.

Closes: https://gitlab.freedesktop.org/drm/intel/issues/683Signed-off-by: Chris Wilson <chris@chris-wilson.co.uk>
Cc: Matthew Auld <matthew.auld@intel.com>
Reviewed-by: Matthew Auld <matthew.auld@intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191208161252.3015727-2-chris@chris-wilson.co.uk

drivers/gpu/drm/i915/i915_vma.c

@@ -1181,7 +1181,7 @@ int __i915_vma_unbind(struct i915_vma *vma)
 	GEM_BUG_ON(i915_vma_is_active(vma));
 	if (i915_vma_is_pinned(vma)) {
 		vma_print_allocator(vma, "is pinned");
-		return -EBUSY;
+		return -EAGAIN;
 	}
 
 	GEM_BUG_ON(i915_vma_is_active(vma));