[HIP] Fix spack detection

Missing or duplicate spack package should not cause error, since
users may only installed llvm/clang package, or users may installed
duplicate HIP package but will use environment variable or compiler
option to choose HIP path.

The message about missing or duplicate spack package is informational,
therefore should be emitted only when -v is specified.

Reviewed by: Artem Belevich

Differential Revision: https://reviews.llvm.org/D102556