Fix typo in INSTALL.md

There was a mismatch in capitalization between the definition and use by
cmake of ROCCLR_DIR

Author: ldrumm

INSTALL.md

@@ -31,7 +31,7 @@ git clone -b $HIP_BRANCH https://github.com/RadeonOpenCompute/ROCm-OpenCL-Runtim
 ```bash
 export HIPAMD_DIR="$(readlink -f hipamd)"
 export HIP_DIR="$(readlink -f hip)"
-export ROCclr_DIR="$(readlink -f ROCclr)"
+export ROCCLR_DIR="$(readlink -f ROCclr)"
 export OPENCL_DIR="$(readlink -f ROCm-OpenCL-Runtime)"
 ```