[fbsync] fixed Gamma casting (#3472)

Summary:
* fixed origin head

* fixed inconsistent casting

* updated functional_tensor.py

Modified the .to() method to convert_image_dtype() method.

* Apply suggestions from code review

Reviewed By: NicolasHug, cpuhrsch

Differential Revision: D26945731

fbshipit-source-id: eab2e30c37bc1d29cae2d0921c869af22b49866a

Co-authored-by: Vasilis Vryniotis <datumbox@users.noreply.github.com>

torchvision/transforms/functional_tensor.py

@@ -227,7 +227,6 @@ def adjust_gamma(img: Tensor, gamma: float, gain: float = 1) -> Tensor:
     result = (gain * result ** gamma).clamp(0, 1)
 
     result = convert_image_dtype(result, dtype)
-    result = result.to(dtype)
     return result