`processFuncOp` asserts that all symbol uses of a function are
`CallOpInterface` operations. This is violated when a function is
referenced by a non-call operation such as `spirv.EntryPoint`, which
uses the function symbol for metadata purposes without calling it.
Fix this by replacing the assertion with an early return: if any user of
the function symbol is not a `CallOpInterface`, skip the function
entirely. This is safe because the pass cannot determine the semantics
of arbitrary non-call references, so it should leave such functions
alone.
Fixes#180416
bcd8819aee