drm/i915: Fix an error code i915_gem_object_copy_blt()

This code should use "vma[1]" instead of "vma".  The "vma" variable is a
valid pointer.

Fixes: 6b050304 ("drm/i915: Convert i915_gem_object/client_blt.c to use ww locking as well, v2.")
Signed-off-by: Dan Carpenter <dan.carpenter@oracle.com>
Reviewed-by: Mika Kuoppala <mika.kuoppala@linux.intel.com>
Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20200911075243.GG12635@kadam
(cherry picked from commit 68ba71e3)
Signed-off-by: Rodrigo Vivi <rodrigo.vivi@intel.com>

drivers/gpu/drm/i915/gem/i915_gem_object_blt.c

@@ -364,7 +364,7 @@ int i915_gem_object_copy_blt(struct drm_i915_gem_object *src,
 
 	vma[1] = i915_vma_instance(dst, vm, NULL);
 	if (IS_ERR(vma[1]))
-		return PTR_ERR(vma);
+		return PTR_ERR(vma[1]);
 
 	i915_gem_ww_ctx_init(&ww, true);
 	intel_engine_pm_get(ce->engine);