Fix missing return in HIPStreamMasqueradingAsCUDA::operator<< (#17961)

Fix missing return in HIPStreamMasqueradingAsCUDA::operator<< (#17961)

Summary:
```
In file included from /var/lib/jenkins/workspace/aten/src/ATen/native/hip/BatchLinearAlgebra.hip:3:
In file included from /var/lib/jenkins/workspace/aten/src/ATen/hip/HIPContext.h:5:
/var/lib/jenkins/workspace/aten/src/ATen/hip/impl/HIPStreamMasqueradingAsCUDA.h:107:1: warning: control reaches end of non-void function [-Wreturn-type]
}
^
1 warning generated.
```
Pull Request resolved: https://github.com/pytorch/pytorch/pull/17961

Reviewed By: houseroad

Differential Revision: D14436421

Pulled By: bddppq

fbshipit-source-id: 962665602178699d7c7b55f4ca7ff1eb72ee0349