Clear HIP_PATH before version detection (#1786)

Don't allow `HIP_PATH` to be propagated to `hipconfig`,
when run by CMake to detect the package version, as it
leads to the wrong version is detected: when there's
already HIP of some different version installed in the
system and `HIP_PATH` points to its location, `hipconfig`
tends to return the version of the installed HIP, rather
than the value defined for the distribution. The compiled
results report wrong version and spoils the rest of the
stack in this case.

CMakeLists.txt

@@ -20,6 +20,7 @@ endmacro()
 # Setup version information
 #############################
 # Determine HIP_BASE_VERSION
+set(ENV{HIP_PATH} "")
 execute_process(COMMAND ${CMAKE_CURRENT_SOURCE_DIR}/bin/hipconfig --version
     OUTPUT_VARIABLE HIP_BASE_VERSION
     OUTPUT_STRIP_TRAILING_WHITESPACE)