ci: define ROCM_DIR in rocwmma build

Author: IMbackK

.github/workflows/build.yml

@@ -1179,6 +1179,7 @@ jobs:
             -DCMAKE_CXX_COMPILER="${env:HIP_PATH}\bin\clang++.exe" `
             -DCMAKE_CXX_FLAGS="-I$($PWD.Path.Replace('\', '/'))/rocwmma/install/include/" `
             -DCMAKE_BUILD_TYPE=Release `
+            -DROCM_DIR="${env:HIP_PATH}" '
             -DGGML_HIP=ON `
             -DGGML_HIP_ROCWMMA_FATTN=ON `
             -DGGML_RPC=ON `