fix set_value when source tensor is fp16 dtype and index is scalar tensor

[Courtesy-Xs]

PR types

Bug fixes

PR changes

Others

Describe

when code set like the following runs in paddle, it will failed because paddle doesn't support assign when source tensor is fp16 type and index is scalar tensor,.
it's restricted by set_value mechanism and its component will be reconstructed soon, so here we just make minor changes for this program runs correctly

import paddle
cls_targets = paddle.full([3,3],0,dtype="float16")
ix1 = paddle.full([1],1,dtype="int64")
ix2 = paddle.full([1],2,dtype="int64")
cls_targets[ix1,ix2]= 1
print(cls_targets)

[paddle-bot]

你的PR提交成功，感谢你对开源项目的贡献!
请关注后续CI自动化测试结果，详情请参考Paddle-CI手册。
Your PR has been submitted. Thanks for your contribution!
Please wait for the result of CI firstly. See Paddle CI Manual for details.

[zhangting2020]

LGTM