fix check for 12.1 (#1383)

Author: ptrblck

conda/build_pytorch.sh

@@ -265,7 +265,7 @@ else
     . ./switch_cuda_version.sh "$desired_cuda"
     # TODO, simplify after anaconda fixes their cudatoolkit versioning inconsistency.
     # see: https://github.com/conda-forge/conda-forge.github.io/issues/687#issuecomment-460086164
-    if [[ "desired_cuda" == "12.1" ]]; then
+    if [[ "$desired_cuda" == "12.1" ]]; then
 	export CONDA_CUDATOOLKIT_CONSTRAINT="    - pytorch-cuda >=12.1,<12.2 # [not osx]"
 	export MAGMA_PACKAGE="    - magma-cuda121 # [not osx and not win]"
     elif [[ "$desired_cuda" == "11.8" ]]; then