drm/i915/gvt: fix uninitialized return in intel_gvt_update_reg_whitelist()

Smatch found an uninitialized variable bug in this code:

drivers/gpu/drm/i915/gvt/cmd_parser.c:3191 intel_gvt_update_reg_whitelist()
error: uninitialized symbol 'ret'.

The first thing that Smatch complains about is that "ret" isn't set if
we don't enter the "for_each_engine(engine, &dev_priv->gt, id) {" loop.
Presumably we always have at least one engine so that's a false
positive.

But it's definitely a bug to not set "ret" if i915_gem_object_pin_map()
fails.

Let's fix the bug and silence the false positive.

Fixes: 493f30cd086e ("drm/i915/gvt: parse init context to update cmd accessible reg whitelist")
Signed-off-by: Dan Carpenter <[e-mail]>
Reviewed-by: Chris Wilson <[e-mail]>
Signed-off-by: Chris Wilson <[e-mail]>
Link: https://patchwork.freedesktop.org/patch/msgid/YA6F3oF8mRaNQWjb@mwanda
(cherry picked from commit 784f70e17e6bc423a04fb6524634a76f68ab1192)
Signed-off-by: Rodrigo Vivi <[e-mail]>

drivers/gpu/drm/i915/gvt/cmd_parser.c

···
 	struct intel_vgpu_submission *s = &vgpu->submission;
 	struct i915_request *requests[I915_NUM_ENGINES] = {};
 	bool is_ctx_pinned[I915_NUM_ENGINES] = {};
-	int ret;
+	int ret = 0;
 
 	if (gvt->is_reg_whitelist_updated)
 		return;
···
 		if (IS_ERR(vaddr)) {
 			gvt_err("failed to pin init ctx obj, ring=%d, err=%lx\n",
 				id, PTR_ERR(vaddr));
+			ret = PTR_ERR(vaddr);
 			goto out;
 		}